Sentence Correction

Today, because of improvements in agricultural technology, the same amount of acreage produces double the apples that it has in 1910.
A. double the apples that it has
B. twice as many apples as it did
C. as much as twice the apples it has
D. two times as many apples as there were
E. a doubling of the apples that it did

OA B

My doubt is with the explanation given in OG double cannot be used as an adverb, so should be replaced by "twice.[/b][/u]

Easier way to solve: take out options A and C, which are in the present tense (since we're talking about 1910). If you have a choice between 'two times' and 'twice/double', 'two times' is never right. That leaves B and E. E is wordy and B correctly uses the idiom 'as many as' to describe the countable noun 'apples'.

my problem is understanding the OG explanation .. why twice can be an adverb and double an adjective...