(A) doubling the increase of
phrase refers back to the subject of the main verb "number of people..."
(B) doubling that of the increase in
"that of" does not have a clear antecedent.
(C) double as much as the increase of
"twice as much as" is the correct form
(D) twice as many as the increase in
"many" cannot be used as comparative for the subject "number", needs to be "much".
(E) twice as many as the increase of
same as D
GGG (Gym / GMAT / Girl) -- Be Serious
Its your duty to post OA afterwards; some one must be waiting for that...