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Answer (A) is correct . Viruses are harmful programs that disrupt memory and processing functions and may destroy data. They spread from network to network, from infected diskettes, or from infected machines. Hence, connecting all networked personal computers through a host computer to outside networks increases the exposure of all of a company’s computers to viruses.

Answer (B) is incorrect because Whether uploaded files are properly edited and validated is independent of whether external links to other networks exist.
Answer (C) is incorrect because Whether data downloaded to the personal computers is sufficiently timely is independent of whether external links to other networks exist.
Answer (D) is incorrect because Whether software maintenance on the personal computers becomes more costly is independent of whether external links to other networks exist.