While performing a preventative maintenance check on a personal computer, a technician notices thatseveralunused expansion card slots have open ports. Which of the following BEST describes why the covers for these card slots should be reinstalled?（）

A. Help limit radio frequency interference (RFI) inside the case.
B. Help ensure proper air flow through the case.
C. Help prevent moisture buildup in the case.
D. Help limit electrostatic discharge (ESD) inside the case.