well why do you need to complete the series? if you need 20A as a major requirement, yes you will have to take it. If you want to use it as a GE, then you need to take it. If 20A is a pre-req, you will need to take it. "Completing a series" means nothing, you need to access if you need the 20A class, as a major requirement, GE requirement, or pre-req.