check this

[mail2sarkar]

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

[chatru]

Out of "A" and E" I will go with A

[scorpion.ks]

"regard as" is the only right idiom here.

Out of A and B.

A is best......"airspace as extending upward".

"the extent" does not fit here.

[sourav106]

Imo E)

[yogesh_kkk]

IMO E "to extend upward" seems correct

[vs8980]

Imo A

[Makumajon]

I opt for E. Though regard takes as, but that should be the case before a noun or an adjective, not before an -ing form.

...regard their space as extended upward as high as provides a better tone. However, I have some reservation about this usage and would rather prefer ommiting [as]. But I find the usage regard...-ing discomforting.

E should be the answer.

[borntorun]

Regard as is the correct idiom ...

IMO A

[alexandro]

ragard as -idiom but pls explain whats wrong with B???

[scorpion.ks]

ragard as -idiom but pls explain whats wrong with B???

Ok, answer this,

airspace can extend upward?
OR
airspace can extent upward?