An anti-craft gun can take a maximum of four shots at an enemy plane moving away from it.The probability of hitting the plane at the first,second,third and fourth shots are 0.4,0.3,0.2,0.1 respectively.what is the probability that the plane is hit when all the four shots are fired?

1) 0.4379
2) 0.6872
3) 0.6976
4) 0.3507