Answer:
D. 60
Explanation:
60 is the only number that 3 and 4 and 5 all go into.
4 does not go into 15, so not answer A.
5 does not go into 12, so not answer B
3 does not go into 20, so not answer C
D is correct. 4 and 5 and 3 all go into 60.