If 6∣a6 \mid a6∣a and 10∣b10 \mid b10∣b, which statement must be true?
30∣(a+b)30 \mid (a + b)30∣(a+b)
60∣ab60 \mid ab60∣ab
15∣a15 \mid a15∣a
5∣a5 \mid a5∣a