In the figure shown the blocks \( A \) and \( C \) are pulled down with constant velocities \( u...

In the figure shown the blocks \( A \) and \( C \) are pulled down with constant velocities \( u \). Acceleration of block \( B \) is:
(a) \( \frac{u^{2}}{b} \tan ^{2} \theta \sec \theta \)
(b) \( \frac{u^{2}}{b} \tan ^{3} \theta \)
(c) \( \frac{u^{2}}{b} \sec ^{2} \theta \tan \theta \)
(d) Zero