IMO E

Whats the OA?

OA is A

"regard as" is the correct idiom so go with A

krisraam wrote: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

Here's my two cents on the issue (and I'm no expert).

"B", "C", and "D" are illogical and ungrammatical, so they can be tossed. "E" is inappropriate because it changes the meaning of the sentence. To say that the "nations regard their airspace to extend upward" literally means that the airspace itself is performing the action of extending, as if it's an animate object.

"A" is the only answer left after eliminating obvious errors. My guess is that "extending" functions as a present participle verbal, which makes it an adjective for "upward".

Just my guess. Please see page 140 of MGMAT SC for more on this.

In short , Regard x as y is idiom

and extent is used when limits are defined here is no limit so extending

+1 for A
regard as is the correct idiom