The correct response is:
The sum or difference of a rational and irrational number is a rational number.
However, it's important to clarify that this statement is actually incorrect in terms of the sum of a rational and an irrational number; the correct statement should be:
"The sum or difference of a rational number and an irrational number is an irrational number."
In defining the closure property, it means that performing a certain operation (like addition or subtraction) on members of a set results in a member of the same set. For rational numbers, their sum or difference remains a rational number. But when you mix a rational number with an irrational number, the result is outside of the rational set, leading to an irrational number.