HELP! Which sentence is not punctuated correctly?

a. I carefully proofread my paper, however, after I printed it out, I found a few errors.

b. If I could, I'd travel to Honolulu, Hawaii; Key West, Florida; and Stockholm, Sweden.

c. Hilary, one of our neighbors, had a book signing last night; she ran out of books.

d. It would be wonderful if you could stop by this afternoon; we have a surprise for you.