Which sentence contains an error?

I've been stuck on this question for a while now, and I'm not really sure what the answer is. Instead of just providing an answer, if you could explain the reasoning, that would be a lot more helpful. Thank you

a. Ten months seem like a lifetime when you're young, but not when you're older.
b. Twenty-five days is a long time at sea.
c. The Sun Also Rises is one of my favorite books. ('The Sun Also Rises' is in italics.)
d. all of the above.

Question

Which sentence contains an error?

I've been stuck on this question for a while now, and I'm not really sure what the answer is.  Instead of just providing an answer, if you could explain the reasoning, that would be a lot more helpful. Thank you

a. Ten months seem like a lifetime when you're young, but not when you're older.
b. Twenty-five days is a long time at sea.
c. The Sun Also Rises is one of my favorite books. ('The Sun Also Rises' is in italics.)
d. all of the above.

.th3_m0nst3r. · Answer

The answer is A because it should be:
Ten months seems like a lifetime when you're young, but not when you're older.