In the following statement, ①The product of two prime numbers must be a composite number; ②The product of two natural numbers must be a composite number; ③If mn=30, then 30 must be divisible by m; ④The fraction with a large fractional unit must be large; ⑤Add or remove 0 after the decimal point, the size of the decimal remains unchanged; how many correct numbers are there?
下面说法中，①两个质数的积一定是合数；②两个自然数的积一定是合数；③若mn=30，则30一定能被m整除；④分数单位大的分数值一定大；⑤在小数点的后面添上或去掉0，小数的大小不变；正确的个数有多少个
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