Best multiple-choice question ever

I wish I had found this question while I was still teaching:

If you choose an answer to this question at random, what is the chance you will be correct?

a) 25%
b) 50%
c) 60%
d) 25%

(Found via Greg Mankiw's blog, which does not have comments. The source he found it on had over 700 comments Some suggested the question would be even better if the answer to c were 0%.)