问两个语法题

wuhaoshady

21: GWD-29-Q41Gas hydrates, chemical compounds of water and natural gas, are increasingly being studied for their potential to be huge reservoirs of energy, possibly causing sea floor instability, and significant contributors to global warming.

A. to be huge reservoirs of energy, possibly causing sea floor instability, and
B. to be huge reservoirs of energy, possibly causing sea floor instability, and even as
C. as huge reservoirs of energy, possibly causing sea floor instability, and
D. as huge reservoirs of energy, and the possible cause of sea floor instability,
E. as huge reservoirs of energy, as possible causes of sea floor instability, and even as(E)
 

According to a recent survey of municipal services, the city’s streets could be cleaner, its fire code be better enforced, and its crime rate reduced if the current administration improved its management practices.

A.  be better enforced, and its crime rate reduced

B. better enforced, and its crime rate reduced （B)

C. could be better enforced, and it could reduce its crime rate

D. better enforced, and its crime rate could reduce

E. could be better enforced, and its crime rate reduce

为什么这两题中前面的AS在平行结构中不能省略而后面的 COULD BE在平行结构中却被省略了？

在什么情况下能省略？

lonelyorchid

如果多个句子的主语相同，且谓语为be，可以省略。

wuhaoshady

好的~谢谢了

aaintw

可是第二题中的三个句子主语都不一样啊 street, code & rate
还有 could 可以一起省掉?
这个省略的语法点从来没见过诶 求指教

lonelyorchid

对于平行列举时, 如果是主系表结构,可以省略(仅限于平行列举)