Final answer:
The answer is 1) Improves performance of code.
Step-by-step explanation:
The correct answer is 1) Improves performance of code. Using rigorous correctness verification of each refinement of the clear box design does not directly improve the performance of the code. This verification process focuses on ensuring the correctness of the design and reducing the number of defects or errors in the code. It does not directly optimize the performance of the code.