两道gwd语法，关于省略，求救

跟秋香打奔儿

3. GWD30-Q3:

Like ants, termites have an elaborate social structure in which a few individuals reproduce and the rest are serving the colony by tending juveniles, gathering food, building the nest, or they battle intruders.



     A.are serving the colony by tending juveniles, gathering food, building the nest, or they battle

B.are serving the colony in that they tend juveniles, gather food, build the nest, or battle

C.serve the colony, tending juveniles, gathering food, building the nest, or by battling

D.serve the colony by tending juveniles, gathering food, by building the nest, or by battling

E.serve the colony by tending juveniles, gathering food, building the nest, or battling
答案是E，为什么E答案的后面几个的by能够省略


21: GWD-29-Q41(
Gas 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

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 evenas
答案也是E，这里as可以省略么？

jinghe

"答案是E，为什么E答案的后面几个的by能够省略"
“by” 如果选择省略, 除了第一个的by, 后面的by 都要省略. 如果选择不省略, 那么每一项前都要把“by” 重复写出.