11. Development of drug resistance is encouraged by________. (A) use of a high enough concentration of the drug to destroy any spontaneous resistant mutants that might arise (B) use of two drugs simultaneously with the hope that each will prevent the emergence of resistance to the other (C) avoidance of indiscriminate(不加區別的) use of drugs (D) widespread use of broad-spectrum drugs (E) using drugs appropriate for the infectious agent being treated