A water tank has the shape of an inverted right circular cone, whose semi-vertical angle is tan−1(21) . Water is poured into it at a constant rate of 5 cubic meter per minute. Then the rate (in m/min), at which the level of water is rising at the instant when the depth of water in the tank is 10 m, is
(A) 5π1
(B) 15π1
(C) π2
(D) 10π1