Tom and Mike are good friends. They are good with children. They want to find jobs in summer vacation. This Friday Tom tells Mike that Sunson School Trip needs teachers to help with sports, music and computer. Mike is glad to know that.
    Tom can play basketball, volleyball, and he can swim. Mike can play the violin, the trumpet, the drums and the guitar, and he can swim,too. Tom and Mike like computers very much. Can they join Sunson School Trip?

夏天常常看到池塘内的鱼出现浮头现象，而中午傍晚则不会出现这种现象，其原因是：

由于生活在水中的鱼和藻类植物进行了一夜的呼吸消耗，会导致水中溶解的氧气含量较低，使鱼的呼吸受影响，而中午和傍晚水中的藻类进行了光合作用，释放出大量氧气，水中氧气含量丰富，所以中午和傍晚很少出现这种现象(   )

小强早上没吃饭，上课时突然大汗淋漓，头晕眼花，你认为补充哪类食物能使他尽快恢复（    ）

根据短文内容，选择正确答案。

    There were many famous explorers during 1400--1600. What were the names of the most famous explorers? What were the major achievements of the famous explorers? This website provides what you want to know.

    Famous Canadian Explorers   The discovery of the New World opened up new colonies(殖民地) in Canada. One of the most famous Canadian explorers was Louis Joliet who explored the Great Lakes area and discovered the Mississippi River.

Famous Spanish Explorers Famous Spanish explorers explored the Caribbean and South America. Just a few famous Spanish explorers conquered (征服) millions of local people who made up the nations of the Incas and the Aztecs. Famous Spanish explorers included Hernando Cortes, Francisco Pizarro, Hernando De Soto, Vasco Nunez de Balboa and Juan Ponce de Leon.

Famous English Explorers The most famous English explorers started their voyages of discoveries during the Elizabethan reign of Queen Elizabeth I. The most famous English explorers included Sir Walter Raleigh, Sir Francis Drake, Sir Martin Frobisher and Sir John Hawkins.

    Famous Portuguese (葡萄牙的) Explorers   The famous Portuguese explorers led the way when it came to exploration. The most famous Portuguese explorers included Ferdinand Magellan, Vasco da Gama, Bartholomeu Dias and Miguel Corte-Real.

下列物质性质的变化规律，与共价键的键能大小有关的是