PMP if you remove defact and another shows because of it why to utilize the change control process?

Hi guys I have the following question in test example of PMPWhile implementing an approved change, a critical defect was introduced. Removing the defect will delay the product delivery. What is the MOST appropriate approach to managing this situation?

A. Utilize the change control process. 
B. Crash the schedule to fix the defect. 
C. Leave the defect in and work around it. 
D. Fast-track the remaining development.

Correct answer is A, why is that the most appropriate?