Which Set of Ordered Pairs Represents a Function from P

Multiple Choice

Which set of ordered pairs represents a function from P to Q? P = {5,10,15,20} Q = {-1,1,3}

A) {(5,3) , (15,1) , (5,-1) , (15,3) }
B) {(15,-1) , (15,1) , (15,3) }
C) {(5,-1) , (10,1) , (10,3) , (15,1) , (20,-1) }
D) {(15,1) , (10,-1) , (5,1) , (10,3) , (15,-1) }
E) {(5,-1) , (10,1) , (15,3) , (20,-1) }