A is corrent. The requirement is to identify the input control that would prevent an incorrect state abbreviation from being accepted. A is corrent because a validity check involves comparison of input to a list of valid items.
B is incorrect because a field check is a control that limits the types of characters accepted.
C is incorrect because a digit verification check is not a recognized control.
D is incorrect because a reasonableness test is used to test a number for a limit or reasonableness.
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