帮忙看看这道题？（求助)

benbenya

A computer is programmed to generate a list of multiples of prime numbers 2,3,5, as show below:

program 1-----list multiples of 2
program 2-----list multiples of 3
program 3-----list multiples of 5

How many integers less than 100 will appear on all of the lists of programs produced above?
(a) None (b)1 (c)3 (d) 5 (e) An infinite number of integers
答案是（c)，为什么？

osha

三个数：30,60,90
就是问100以内2，3，5的公倍数有多少个。