Which of the Following BEST Describes Why an Air Gap

Which of the following BEST describes why an air gap is a useful security control?

A) It physically isolates two or more networks, therefore helping prevent cross contamination or accidental data spillage.
B) It requires that files be transferred via USB instead of networks that are potentially vulnerable to hacking, therefore preventing virus infections.
C) It requires multiple systems administrators with different credentials, therefore providing separation of duties.
D) It provides physical space between two interlocking doors, therefore providing additional control from unauthorized entry.