34. GWD30-Q34:

Books in
European libraries last longer than books in libraries in the United States
            because, although the climate
in Europe is fairly humid, libraries there are not subjected to the extremes of
temperature and humidity that damage collections in the United States.

A.   
because, although the climate in Europe is fairly humid, libraries there are not subjected
to the extremes of temperature and humidity that

B.   
because, although the climate in Europe is fairly humid, libraries there are not subject
of the extremes of temperature and humidity as those that

C.   
because, although the climate in Europe is fairly humid, libraries there are not subjected
to the extremities of temperature and humidity as

D.   
because the climate in Europe
is fairly humid, but still libraries there are not subject of the extremes of
temperature and humidity as

E.    
because the climate in Europe
is fairly humid, but libraries there are not subjected to the extremities of
temperature and humidity such as those that

答案是a，其他选项中句尾的as those that错在哪里呢？

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.   
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

答案是e,我选了c。e中的as possible causes是复数啊，为什么呢？

多谢指点！

 as possible causes of sea floor instability, and even
            as  significant contributors to global warming.--》对称

extremities of temperature and humidity as damage collections 对称，不需要用those of