Choose the sentence that is correctly punctuated.

A. First, you rinse any dirt off the onion, then you carefully slice it.

B. The exact same as A...not sure why...

C. First, you rinse any dirt off the onion; then you carefully slice it.

D. First, you rinse any dirt off the onion then you carefully slice it.
I think it's A, but since A and B are the same I'm confused.