Emerging viruses arise by?

a. mutation of existing viruses.

b. the spread of existing viruses to new host species.

c. the spread of existing viruses more widely within host species.

d. all of the above

e. none of the above

Emerging viruses arise by?antispyware

d all of the above

Emerging viruses arise by?best antivirus software

none of the above
Think of examples:

a: flu virus (avian flu, swine flue, ...)

b: AIDS, which originally spread to man from monkeys

c: Things like smallpox, originally a European disease that was spread accidentally and intentionally among indians in the Americas

So the answer is certainly d