请教一道Prep上的概率题

92，On his drive to work, Leo listens to one of three radio stations, A, B, or C.  He first turns to A.  If A is playing a song he likes, he listens to it; if not, he turns to B.  If B is playing a song he likes, he listens to it; if not, he turns to C.  If C is playing a song he likes, he listens to it; if not, he turns off the radio.  For each station, the probability is 0.30 that at any given moment the station is playing a song Leo likes.  On his drive to work, what is the probability that Leo will hear a song he likes?

(A) 0.027

(B) 0.090

(C) 0.417

(D) 0.657

(E) 0.900

ans：D

请问这种题目怎么做？有公式吗？

D

他听到喜欢的songs的可能性:1st stataion + 2nd station + 3rd station

0.3 + 0.7*0.3 + 0.7*0.7*0.3 = 0.657