If n is a multiply of 5 and n=p2q, where p and q are prime number, which of the following must be a multiply of 25?
A p2
B q
D p2q2
E p3q
答案是d
n是5的倍数,表示p,q至少有一个是5的倍数,p2q2则能保证是25的倍数,因为不管p还是q为5的倍数,其平方必然是25的倍数。
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