The sea is home to billions of plants and animals. Many live only near the sunlit surface. Oceanographers sort marine (海洋的) living beings by dividing them into two main groups: plants and animals.

There are two general types of plants found in the ocean, those having roots that grow in the ocean bottom and those not having roots which simply float around with water. The rooted plants in the ocean are only found in shallow waters because there is not enough sunlight to maintain photosynthesis (光合作用) in deeper waters. Since sunlight does not pass more than a few hundred feet into the ocean, most of the ocean is unable to support rooted plants.

The most plants in the ocean are known as phytoplankton (浮游植物群落) . These are usually single-celled, small floating plants that float throughout the surface waters of the ocean. To grow, phytoplankton need nutrients from the sea water and lots of sunlight.

Marine animals are divided into three groups: zooplankton, nekton, and benthos. Zooplankton are floating animals and are usually small; however, they can grow to fairly large size. The jellyfish and the Portuguese man-of-war are examples of larger types of zooplankton which are unable to move themselves effectively.

Nekton are the free swimmers and probably the largest part of familiar animals found in the ocean belong to this class. Common fishes, octopuses, whales, eels and squid are all examples of nekton.

The third type of sea animals spends their entire life on the bottom of the ocean. This group of marine animals is called benthos. Some of these creatures, such as lobsters and snails, may be able to move about on the bottom but their lifestyle is so closely linked with the ocean floor that they are unable to survive away from this environment.

【小题1】What does the text mainly introduce?

A．Marine plants and marine animals.	B．Two types of sea plants.
C．Three kinds of sea animals.	D．Small and big animals in the ocean.

【小题2】Why can’t we find the rooted plants in deep waters of the ocean?

A．Because there are too many rocks at the bottom of the ocean.

B．Because the rooted plants can’t stand the coldness of the ocean.

C．Because there is not enough sunlight for them in deep waters.

D．Because the rooted plants need more sunlight than plants which have no roots.

【小题3】One of the characteristics of zooplankton is that __________ .

A．they are small and never grow to large size

B．some of the zooplankton can’t swim quickly

C．they can swim freely in deep waters of the ocean

D．they need more sunlight than other animals in the ocean

【小题4】According to the last paragraph, we can conclude that __________ .

A．benthos live on the surface of the ocean water

B．some of the benthos can’t live without the ocean floor

C．benthos spend most of their time swimming in the ocean

D．benthos can move about in the middle of the sea water

   Winter begins in the north on December 22nd. People and animals have been doing what they always do to prepare for the colder months. Squirrels (松鼠), for example, have been busy gathering nuts from trees. Well, scientists have been busy gathering information about what the squirrels do with the food they collect.

They examined differences between red squirrels and gray squirrels in the American state of Indiana. The scientists wanted to know how these differences could affect the growth of black walnut (黑胡桃) trees. The black walnut is the nut of choice for both kinds of squirrels. The black walnut tree is also a central part of some hardwood forests.

Rob Swihart of Purdue University did the study with Jake Goheen, a former Purdue student now at the University of New Mexico. The two researchers estimate that several times as many walnuts grow when gathered by gray squirrels as compared to red squirrels. Gray squirrels and red squirrels do not store nuts and seeds in the same way. Gray squirrels bury nuts one at a time in a number of places. But they seldom remember where they buried every nut. So some nuts remain in the ground. Conditions are right for them to develop and grow the following spring. Red squirrels, however, store large groups of nuts above ground. Professor Swihart calls “death traps for seeds”.

Gray squirrels are native to Indiana. But Professor Swihart says their numbers began to decrease as more forests were cut for agriculture. Red squirrels began to spread through the state during the past century.

The researchers say red squirrels are native to forests that stay green all year, unlike walnut trees. They say the cleaning of forest land for agriculture has helped red squirrels invade Indiana. Jake Goheen calls them a sign of an environmental problem more than a cause.

【小题1】The study done by Rob Swihart and Jake Goheen is to ________.

A．find out the living conditions for squirrels

B．learn squirrels’ influence on black walnut trees

C．do something to get rid of squirrels

D．save the forests in the American state of Indiana

【小题2】The difference between gray squirrels and red squirrels mainly lies in ________.

A．the way they gather the walnut

B．the time they have winter sleep

C．the place they have winter sleep

D．the place they store the walnuts

【小题3】When Professor Swihart says “death traps for seeds”, he actually means that ________.

A．red squirrels eat more nuts than gray squirrels

B．gray squirrels and red squirrels will have severe fights

C．nuts above the ground will not develop into plants

D．seeds can be traps for other animals in the forest

【小题4】According to the passage, which of the following is true?

A．The black walnut is equally attractive to both gray and red squirrels.

B．Gray squirrels do more harm to the forest than red squirrels.

C．Red squirrels and gray squirrels have helped the spread of walnut trees.

D．The cleaning of forest land benefits red squirrels directly.

   According to a study published last week in the journal Science，scientists have found a way to change a plant's genes（基因）in order to make it use sunlight more quickly. Someday，the results could increase the amount of food produced around the world.

By changing a plant's genes，the scientists were able to increase leaf growth on plants by 14-20 percent. Specifically，scientists changed the plant's protective（保护的）system. “Normally，this system is activated when a plant gets too much sunlight，”said scientist Krishna Niyogi，co-author of the study. “When the plant senses the light，it gets rid of extra energy and creates more leaves. When the plant is in the shade，the protective system is turned off. But the process is slow.”

Stephen Long is the lead author of the study. He compared a plant's protective system to light-adjusting glasses.“When a person wears the glasses outside during the day，the lenses（镜片）darken and lighten depending on how sunny it is. Plants do the same thing，”he said.“But in plants the adjustment can take anywhere from 10 minutes to an hour. This makes it hard for plants to get the right amount of sunlight needed to create food.”

The new study sped up the process. By changing the plant's genes，it's more quickly than normal to turn on and turn off the protective system. As a result，leaf growth on the plants scientists used in the study increased. Leaf growth on two plants increased by 20 percent, while leaf growth on a third plant increased by 14percent. Scientists conducted the study on tobacco plants. But they thought the genetic modification would produce the same results in corn or rice.

【小题1】What does the plant's protective system need to keep activated?

A．Mild shade.	B．Leaf growth.
C．Genetic changes.	D．Enough sunlight.

【小题2】What does the underlined word“modification”in Paragraph 4mean?

A．Development.	B．Decoration.
C．Change.	D．Copying.

【小题3】What can we infer from this text?

A．Changing how a plant uses sunlight could mean more food in the future.

B．When the plant is in the shade, its protective system is turned off slowly.

C．Too much sunlight will damage plants' protective system.

D．It is hard for plants to create food without enough sunlight.

短文改错
When the soldiers are being attacked, they are worrying. Then a good idea occurs on to an officer. He writes a short message on a piece of paper and rolls it up. After attached it to a pigeon's leg, he makes the pigeon loose. The pigeon immediately flies into the air and disappeared in the dark.
Why does an officer choose a pigeon to send an important message? Pigeons have a wonderful sense of direction and can find its way home over long distances. That's why pigeons have used since ancient times to carry news. However, it was in war which people found their greatest use. During both World War I and World War Ⅱ, pigeons were employed by armies to carry messages to or from the front lines, saving the lives of many soldier.