Read the following SAT test question and then click on a button to select your answer.

f(2n) = 2f(n) for all integers n
f(4) = 4
If f is a function defined for all positive integers n, and f satisfies the two conditions above, which of the following could be the definition of f?

(A) f(n) = n-2
(B) f(n) = n
(C) f(n) = 2n
(D) f(n) = 4
(E) f(n) = (2n)-4

来源:可可英语 http://www.kekenet.com/sat/201505/375692.shtml