阅读理解：
Drug Resistancet Fades Quickly in Key Aids2 Drug
One of the main weapons to prevent mother-to-child transmission of the AIDS virus during birth is the drug nevirapine3. But when nevirapine is used alone just once, HIV4 starts becoming resistant to it. Research in Botswana shows that the resistance is not long lasting and that this affordable drug does not have to be abandoned forever by infected mothers who have already taken it.
The problem is that HIV resistance builds against it quickly when used alone just once because other drugs are not present to kill the virus particles that survive nevirapine. This renders the drug less effective in later combinations for treating women after their baby is born. But the new study from Botswana shows that nevirapine can make a comeback for these women if they wait until the resistance subsides.
The study published in the New England Journal oJ Medicine9 shows that waiting at least six months means that HIV-positive women are 70 percent more likely to benefit from nevirapine-based drug combinations again than women who get them sooner. An official with the U.S. government health agency that helped fund the study calls it very important.www.zcyy8.CoM
Shahin Lockman in Boston says the problem of nevirapine resistance should diminish now that12 more and more people are receiving combinations of AIDS drugs under expanded U. S. and international programs to deliver them to Africa and other regions hard hit by the virus.：
A It is a broad-spectrum antibiotic and kills all kinds of bacteria.
C It prevents the transmission of the AIDS virus and protects one from heart attack.
2. Why does HIV resistance against nevirapine build very quickly even when the drug is used alone just once?
B Because there may not be a susceptibility test before using the drug.
D Because there are too many mutations of HIV for nevirapine to deal with.