The number of vehicles on the road classified as "light trucks" in the United States
increased by more than twice from 1980 to 1992.
a) increased by more than twice
b) increased more than two times
c) more than doubled
d) was more than doubled
e) had more than doubled
Meaning :
Number doubled/ More than doubled during certain period of time.
POE
a) increased by more than twice
Twice is adverb, Needs verb to modify. cannot be used as an object for preposition "by". (Some official question also test the same concept will edit the post if i manage to find it). Incorrect.
b) increased more than two times
Redundant - Increased more than two times - Sounds unidiomatic. Incorrect.
c) more than doubled
Correct - Subject (Number) Verb (doubled) pair is correct. "More than" is adverb. It is same as Number (fluff/Adverb) doubled during certain period.
d) was more than doubled
number was more than doubled during certain period. That is not intended meaning. we wanted to say, number doubles itself during certain period. Also, it is in passive voice.
e) had more than doubled
Unnecessary use of had , That is not intended meaning. we wanted to say, number doubles itself during certain period