Two fixed frictionless inclined planes making an angle 30° and 60° with the vertical are shown in the figure. Two blocks A and B are placed on the two planes. What is the relative vertical acceleration of A with respect to B?

(a) 4.9ms–2 in vertical direction
(b) 4.9ms–2 in horizontal direction
(c) 9.8ms–2 in vertical direction
(d) zero