A computer runs normally for several minutes, gradually runs slower, and then shuts down without...

The correct answer is B. Replacing the fans .

According to CompTIA A+ Core 1 220-1201 objectives under Hardware and Troubleshooting:

A computer that gradually slows down and then shuts down without warning is often experiencing overheating .

Overheating can occur when cooling fans fail or dust accumulates, preventing proper airflow. Replacing or cleaning fans restores cooling and prevents thermal shutdowns.

Why the other options are incorrect:

A. Upgrading the memory: Would improve system performance if there is insufficient RAM but does not prevent thermal shutdowns caused by overheating.

C. Adding drive space: Helps with storage capacity but does not affect CPU/GPU heat or thermal shutdown.

D. Swapping the power supply: Would address power delivery issues, but the scenario describes gradual slowdown before shutdown, which is characteristic of thermal issues rather than immediate power failure.