求助，有题不会，请指教

4. If n
is a positive integer and  n*2（n的平方）is divisible by 72, then the largest positive integer that must
divide n is

A. 6       
B. 12           C. 24        D.36       E. 48

正确答案是：B

72=6×6×2，那么N里面肯定有6和2啦，所以the largest positive integer that must divide n只能是12啦！