Which statement best defines one-to-one correspondence?

• A. Members of one set can evenly be matched to members of a second set.
• B. The order of numbers matters when counting.
• C. Two sets have the same size but not necessarily paired.
• D. A match can assign multiple elements in one set to a single element in the other.

Answer: (A)

One-to-one correspondence is when every element in the first set is paired with exactly one element in the second set, and that second-element is paired back with exactly one element from the first set. The statement that members of one set can evenly be matched to members of a second set best captures this because it conveys a complete, equal pairing where each item has a unique partner on the other side. The other ideas don’t fit: counting order is about sequence, not how elements pair between sets; having the same size without guaranteeing pairing misses the requirement of a matched partner for every element; and allowing multiple elements to map to the same element breaks the one-to-one nature by creating many-to-one mappings.