求解语法一道

gzguohongbo

1.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
答案为A，我语感上选对了，但是说不清楚，这题是考as···as的对称吗