When implementing a solution to a problem, which of the following is the BEST course of action to take?

A.
Replace all components simultaneously to ensure that the system is functional.

B.
Replace all hardware associated with the problem first to eliminate the possibility of hardware and move onto software.

C.
Purchase new parts for the system to confirm that they function.

D.
Implement one change at a time, reversing the change if it has not resolved the problem.