C

This is an emphasis sentence pattern. Equivalent to BA.

There is also a negative forward (not until's not).

Converted into ordinary sentence patterns is:

It was not until he came back from Africa that he met the girl he wanted to marry.

D's first choice is not grammatical. It has two subjects: it and him, and its meaning is also very strange: only when he comes back from Africa and meets the girl he wants to marry. It only destroys grammar here, and when does it destroy meaning here? Of course not.