A composite number is a number that has more than 2 factors.
A prime number is a number who only have 2 factors (1, and itself)
Factors:-
9 = 1, 3, 9 = composite
2 = 1, 2 = prime
15 = 1, 3, 5, 15 = composite
21 = 1, 3, 7, 21 = composite
So, the prime #'s in this set are 2. The composite #'s in this set are 9, 15, and 21.
Hope I helped ya!!
I'd personally go with A and C, The rest don't make too much sense. Don't count on my answer just yet though.
