题目

 It was decades ago ______ I was in my teens ______the Chinese government decided to reform the social system.     A. that: which       B. when; that           C. which: that          D. that; when 答案：B14．下列关于“探究培养液中酵母菌种群数量的变化”实验的叙述，正确的是（　　）A．为保证酵母菌正常生长，要定期更换培养液B．为保证酵母菌正常繁殖，培养容器必修敞开C．为解决逐个计数的困难，可采用抽样检测法D．为保证实验中计数准确，每次取样必须稀释