Sentence Correction

According to the National Science Foundation, in 2003 there were 198,113 female science and engineering graduate students, almost 42% of the graduate students in those fields, twice as much as 1981.
A twice as much as 1981
B twice as many as 1981
C double the figure for 1981
D double what it was in 1981
E a number double that of 1981’s

This is a question from MGMAT Online CAT, the answer is C[spoiler]

IMO the "for" is inappropriate... any pointers?

According to the National Science Foundation, in 2003 there were 198,113 female science and engineering graduate students, almost 42% of the graduate students in those fields, twice as much as 1981.
A twice as much as 1981

OUT --comparing with 1981 rather than its figure

B twice as many as 1981
OUT --comparing with 1981 rather than its figure

C double the figure for 1981

Correct
D double what it was in 1981

what it was ..bit awkward..( not precise enough)
E a number double that of 1981’s

i would prefer figure rather than number..OUT

A twice as much [color=red]as 1981 [/color]
B twice as many [color=red]as 1981[/color]
C double the figure for 1981
D double what[color=red] it[/color] was in 1981
E a number double that of [color=red]1981’s[/color]


imo:C