A mold having dimensions 100 x 90x20 (all in mm) is filled with molten metal through a gate with height ‘h’ and C.S area A, the mould filling time is t1. The height is now quadrupled and the cross sectional area is halved. The corresponding filling time is t2. The ratio t2/t1 is
(a) 1/√2 (b) 1
(c) √2 (d) 2