An anti aircraft gun take four shots at an enemy plane moving away from it. The probability of hitting the plane at the first, second, third and fourth shot are 0.4, 0.3, 0.2 and 0.1 respectively. The probability that the gun hit the plane is :- (A) 0.25 (B) 0.21 (C) 0.16 (D) 0.6976