Which of the following statements is correct about the early exercise of American options?
a) It is always optimal to exercise an American call option on a non-dividend-paying stock before the expiration date.
b) It can be optimal to exercise an American put option on a non-dividend-paying stock early.
c) It can be optimal to exercise an American call option on a non-dividend-paying stock early.
d) It is never optimal to exercise an American put option on a non-dividend-paying stock before the expiration date.