Macro viruses written in Visual Basic for Applications (VBA) are a major problem because

A.
Floppy disks can propagate such viruses.

B.
These viruses can infect many types of environments.

C.
Anti-virus software is usable to remove the viral code.

D.
These viruses almost exclusively affect the operating system.

Explanation:
VBA is typically Windows OS base, so Unlikely many types of environments, but impact the OS
(need a real reference source to justify this though).