OG11-37

一道不难的题, 但总觉得没有彻底想通.

37. If a positive integer n is divisible by both 5 and 7, then n must also be divisible by which of the following

I. 12 II.35 III.70

answer is II.35 only.

但是70 可以分解为  7*5*2, 为什么不包括 70?   请高手指点一下. 谢谢!