问题
选择题
Quantities of water________for cooling in the only 
one of the plants that________steel. [ ]
A. has been needed; produces
B. are needed; produces
C. is needed; produce
D. have been needed; produce
答案
答案：B
、－CH＝CH－两种结构单元组成，且它们自身不能相连，该烃分子中C、H两原子物质的量之比是 [ ]