A weightless rod of length 2l carries two equal masses 'm', one tied at lower end A and the other at the middle of the rod at B. The rod can rotates in vertical plane about a fixed axis passing though C. The rod is released from rest in horizontal position. The speed of mass B at the instant , rod become vertical is
(1) square(3gl/5)
(2) square(4gl/5)
(3) square(6gl/5)
(4) square(7gl/5)