The funny thing is, that after a bit of reasoning, I come to the conclusion that this is not a multiple choice question. If you chop up the question into two parts you'll see this.
Edit: Pretty sure it should be zero, as:
P(.25)=.5
P(.5)=.25
P(.6)=.25
Even if C is 0 then:
P(0)=.25
Therefore the chance is 0. In addition, the chance is zero for every C.
Edit2: I just googled the question, seems to be a lot of debate on this. Apparently no-one really seems to agree.