题目内容：
Why does HIV resistance against nevirapine build very quickly even when the drug is used a-lone just once?
A．Because the drug is not strong enough to kill all of the HIV in the body.g. Because there may not be a susceptibility test before usingthe drug. B．Because other drugs are not present to kill the virus particles that survive nevirapine.
C．Because there are too many mutations of HIV for nevirapine to deal with.
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