The Main Reason There Are Very Few Effective Antiviral Drugs

The main reason there are very few effective antiviral drugs is because

A) viruses cannot be cultured in the laboratory to determine their sensitivity to antiviral drugs.
B) viruses are too simple to be attacked by a chemical compound.
C) viruses use the host's metabolic machinery so there are few points of selective attack.
D) viruses are difficult to identify under the light microscope.
E) it is too expensive to develop and test them.