问题
单项选择题
在蛋白质分子中连接两个相邻的氨基酸残基的共价键是（）
A．氢键
B．离子键
C．二硫键
D．肽键
E．酯键
答案
参考答案：D
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在蛋白质分子中连接两个相邻的氨基酸残基的共价键是（）
A．氢键
B．离子键
C．二硫键
D．肽键
E．酯键
参考答案：D
| 阅读理解。 |
| The world is not only hungry, but it is also thirsty for water. This may seem strange to you, since nearly 70% of the earth's surface is covered with water. But about 97% of that is sea water, or salt water. Man can only drink and use the other 3%-fresh water from rivers, lakes, underground, and other sources (资源). But we cannot even use all of that. However, our need for water is becoming larger almost day by day. We should take steps (措施) to deal with (对付; 处理) this problem now and in this way we can avoid (避免) a serious worldwide water shortage later on. We all have to learn how to stop wasting our valuable water. One of the first steps is to develop (开发; 发展) ways of reusing it. Today in most large cities, water is used only once and then sent out into a sewer system (下水道). From there it returns to the sea or runs into underground places. But even if (即使) every large city reused its water, we still would not have enough. All we have to do, to make use of (利用) sea water in the world, is to remove (去除) the salt. But it is not an easy thing. |
| 1. The world is thirsty for water because _______. |
[ ] |
| A: man hasn't got enough food to eat. B: we haven't got enough fresh water. C: only 70% of the earth's surface is water. D: more water is sent into sewer system. |
| 2. The underlined word "valuable" means______. |
[ ] |
| A: much and salty B: rare (稀罕) C: cheap and useful D: much and helpful |
| 3. What should we do if we want to have enough fresh water? (a) Make full use of the sea water. (b) Carry salt water into lakes or rivers. (c) Try to save the fresh water as much as possible. (d) Do our best to use the water again. (e) Drink and use all the water on the earth's surface. |
[ ] |
| A: (c) and (e) B: (a) and (d) C: (a), (c) and (d) D: (b), (d) and (e) |
| 4. The best but the most difficult way to solve the water problem of the world is to . |
[ ] |
| A: remove the salt from the sea water B: make the water in the cities clean C: take water from underground D: make the need for water smaller |
| 5. The best title of this passage is ______. |
[ ] |
| A: the World Is Not Only hungry but Also Thirsty B: We Should Make Steps to Deal with the Water Problem C: The World's Water Problem D: The Fresh Water Is Still Enough |