Blocks A and B, of masses m and m, are at rest on a frictionless surface, as shown above, with block A...

8. Blocks A and B, of masses m and m, are at rest on a frictionless surface, as shown above, with block A fixed to the table. Block C of mass m is suspended by a string that is tied to block B over an ideal pulley. Which of the following gives the magnitude of the force exerted by block A on block B?
A) mBg
B) mCg
C) (mA mC / mA + mB) g
D) (mB mC / mA + mB) g