Tip: See my list of the 
MostA common mistake: English learners see “a couple”, which is in the singular, and assume that the verb must be in the singular, too. However, the same we’ve said about collective nouns applies to expressions like “a couple” and “a few” as well.
Although the noun itself is in the singular, what it really describes is more than just one thing or person. It doesn’t matter whether you mean literally a couple, i.e. just two people or things, or you use “a couple of” synonymously to “a few”; it represents a plural idea, so the correct form is:
Only when “a couple” is not followed by “of” and is used to mean “a pair of people”, and you refer to the couple as a whole, not just to individual persons who constitute it, you should treat it as being singular:
