(2015·临沂)近年来,抗生素的滥用致使很多病细菌具有一定的抗药性。根据达尔文的进化论分析,而药细菌越来越多的主要原因是 A、抗生素的质量下降,杀菌能力低 B、细菌为了适应环境,产生了抗药性变异 C、抗生素选择了发生耐药变异的个体生存下来 D、耐药细菌繁殖能力比不耐药细菌繁殖能力强____________ great help, I could get rid of all the difficulty and succeeded. A. Offered B. Having offered C. Being supplied D. Having supplied