请教2条白勇语法题

3. Computers are becoming faster, more powerful, and more reliable, and so too are modems, they are the devices to allow two or more computers to share information over regular telephone lines.
(A) so too are modems, they are the devices to allow
(B) so too are modems, the devices that allow
(C) so too modems, the devices allowing
(D) also modems, they are the devices that allow
(E) also modems, which are the devices to allow
            

答案是B,请问E少are以外，其他还有哪里有问题吗？

16. Migraine, the most debilitating common form of headache, afflicts perhaps 18 million Americans, who collectively lose 64 million workdays a year, and they cost the nation $50 billion in medical expenses and lost work time.
(A) year, and they cost the nation $50 billion in medical expenses and lost
(B) year and thus cost the nation $50 billion in medical expenses and lost
(C) year, so as to cost the nation $50 billion in medical expenses and lost
(D) year that costs the nation $50 billion in lost medical expenses and
(E) year, which thus cost the nation $50 billion in lost medical expenses and

答案是B，请问C为什么不对？

谢谢！

3. E中如果加上are的话也不对，B中在句子前用so引导倒装省略句，但also没有这个功能；

16. so as to 应该是表主观目的的。

16还错在year, so as to cost the nation $50 billion in medical expenses and lost
to cost 与lost不平行对称