Answer:
B
Step-by-step explanation:
10 and 14 don’t have any common factors except for 1 and 2, which isn’t 5
13 and 21 don’t have any common factors except for 1, which isn’t 3
14 and 21 don’t have any common factors except for 1, which isn’t 3
15 and 10 have common factors which are 1 and 5, and 5 is the number we need because 5 = 5
