In the figure, the pulley P moves to the right with a constant speed u. The downward speed of A is `v_(A)`, and the speed of B to the right is `v_(B)`.
A. `v_(B) = v_(A)`
B. `v_(B) = u +v_(A)`
C. `v_(B) +u =v_(A)`
D. The two blocks have accelerations of the same magnitude.