In a(n) primary, only declared members of the party can vote on that party's candidate.
a) closed/nonpartisan
b) open/runoff
c) closed/direct
d) open/direct

It needs to be a closed primary: only in a closed primary the only people to vote are the party members.

A nonpartisan primary is a primary where the candidates do not need to be from that party.- this is not what the question is asking for.
So the correct answer is C) closed/direct.

Bob: coke is baby pandas.jim: what? how do you figure that coke is baby pandas? bob: because this book says so.jim: how do we know the book is correct? bob: because it says that coke is baby pandas.jim: how does that prove the book's accuracy? bob: because it's statement involving coke and baby pandas is correct, therefore it is accurate.jim: how do we know that it's correct? bob: because we have concluded that the book is accurate, and therefore the statement is correct.therefore, coke is baby pandas.