prep DS 2-2（选项2啥个意思）

2.    140-!-item-!-187;#058&000076

If k is a positive integer, is k the square of an integer?

(1) k is divisible by 4.

(2) k is divisible by exactly four different prime numbers.

请问选项（2）说的什么意思？

多谢多谢！