求助一道题

lebenkong

Q25:

If the number 52,1n9, where n represents the tens digit, is a multiple of 3, then the value of n could be which of the following?

A. 6

B. 5

C. 3

D. 1

E. 0

Answer: d

没看明白是什么意思  。。请牛牛 解释解释

monacopig

if 521n9 is the multiple of 3, then 5+2+1+n+9 is the multiple of 3, then n= 1, 4 , 7 (1<n<9)