Which set is closed under subtraction?

Rational numbers are closed under subtraction: subtracting one rational number from another always gives a rational number. For example, 3/4 − 1/2 = 1/4. Whole and natural numbers can have a negative difference, and irrational numbers can subtract to give a rational number, such as √2 − √2 = 0. So the correct choice is C, the set of rational numbers.

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