Step 1: Understanding the scenario.
The problem describes a situation where Matilda borrows a necklace made of real diamonds, but she returns a necklace made of artificial diamonds. This means the borrowed item is of higher value than the returned one.
Step 2: Analysis of options.
(A) Matilda borrowed a necklace of real diamonds, but returned a necklace of artificial diamonds: Correct. This matches the description given in the problem.
(B) Matilda borrowed a necklace of real diamonds and returned a necklace of real diamonds: Incorrect. This does not match the scenario as the returned necklace was not made of real diamonds.
(C) Matilda borrowed a necklace of artificial diamonds and returned a necklace of artificial diamonds: Incorrect. This does not fit the scenario as the necklace borrowed was made of real diamonds, not artificial diamonds.
(D) Matilda borrowed a necklace of artificial diamonds, but returned a necklace of real diamonds: Incorrect. This is the reverse of what happened in the scenario.
Step 3: Conclusion.
The correct statement is (A), where Matilda borrowed a necklace of real diamonds but returned a necklace of artificial diamonds.