I didn' t manage to do it _____ you had explained how.

A. until           B. unless              C. when                  D. before

I didn’t manage to do it ______ you had explained how.

A. until　　 　B. unless　　 C. when　 　　　D. before

I didn’t manage to do it _____ you had explained how.

A. until 　 B. unless　 C. when 　 D. before

I didn’t manage to do it _____ you had explained how.

A. until 　 　　B. unless　　 C. when 　 　 D. before

I didn’t manage to do it_________ you had explained how.
A. unless                       B. until?
C. when                        D. since