维生素C有酸性，是因为其化学结构上有（）。
A.无机酸根
B.羰基
C.多羟基
D.共轭系统
E.连二烯醇
参考答案：E
根据句意及首字母提示补全单词。
1. With the d_____ of China, all the children can go to school.
2. The two sides failed to reach a_____.
3. Some spaceships have gone b_____ the solar system.
4. We are here to p_____ the public with a service.
5. What's the i_____ of television on children?
如何理解“清廉”？
