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（A）
(E) to extend
为什么不是B？extent名词，后面的upward as high as an aircraft can fly 修饰extent
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发表于 2006-2-12 05:15:00
