I simply and copy and pasted it from a Physics GRE practice test without giving it the multiple choice answers [1].

The choices were:

(A) 2Q

(B) Q

(C) 0 <--- right answer

(D) -Q

(E) -2Q

Here is the answer it gave: "When a positive charge is placed a distance L above an infinite grounded conducting plane, the charge will cause an excess of positive charge to accumulate on the side of the plane closest to the charge, and a deficiency of positive charge on the opposite side of the plane. The total charge induced on the plane is the sum of the excess and deficiency of positive charge, which is equal to zero. Therefore, the total charge induced on the plane is zero."

[1] http://sites.apam.columbia.edu/courses/apph4903x/exam_GR0177.pdf