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.

   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.

   Dogs will do absolutely anything for the people they love，and for one North Carolina dog，that meant _________his own life in order to save his best friend.

This past Saturday morning，a deadly fire _________in an apartment building that left multiple families and their beloved pets _________inside waiting for help to arrive. "My wife got a phone call and it was very  very _________because she had her on the speakerphone and my daughter was very  very _________ and she was screaming that the apartment was on fire，"said Mare Martinez，whose daughter Karina was _________in the apartment when the fire started.

Karina had no _________ that her life was in danger until her dog，a 2-year-old German Shepherd named Riddick，woke her up with his panicked _________."Her dog wouldn't settle down so she called him up on her bed to cuddle（依）him，"Martinez explained." _________，he was still sitting up and __________barking at the wall."

After __________there was a fire，Riddick helped guide Karina to safety. "She went down the landing（楼梯平台）because there were already flames，but the dog got __________and went back up and would not come down，"said Martinez __________，she couldn't get Riddick to come back down and he __________before firefighters could rescue him." He was her best friend，they were __________and he did what he was supposed to do. He __________and took care of her when she was in danger.”

"The great Greenville Fire and Rescue department of the city did us very  very __________.They made this even just a little bit more tolerable，"said Martinez，who was __________when they went into the building and got back Riddick's __________ so they could give him a proper __________.

   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.