请问885-04-12&23
12. Most nations regard their airspace as extending upward as high as an aircraft can fly; no specific altitude, however, has been officially recognized as a boundary.
(A) as extending
(B) as the extent
(C) to be an extent
(D) to be an extension
(E) to extend
这题划线的UPWARD不在A里, 我想问,B选项为什么不对? 原文划线部分怎么理解才好呢?
extingding应该是adj吧，什么叫regard sth as adj as adv as....
请问这句话是什么意思啊谢谢 | 
