71. A small object of mass m is suspended from a fixed point O by a light, inextensible cord.The object is raised until the cord is horizontal and then released. It moves in an arc of acircle as shown in the figure above. When it passes through its lowest position at point P,the tension in the cord is__________ .
(A) 3mg.
(B) 2mg.
(C) 1mg.
(D) 0mg.