23. Three blocks of masses 3m,2m, ands are connected to strings A,B, and C as shown above. The blocks are pulled along a rough surface by a force of magnitude F exerted by string C. The coefficient of friction between each block and the surface is the same. Which string must be the strongest in order not to break?
(A) A
(B) B
(C) C
(D) They must all be the same strength.