单项选择题Great changes have taken place in that school. It is no longer ____ it was 20 years ago, ____ it was so poorly equipped.A. what; whenB. that; whichC. what; whichD. which; that
单项选择题实验的定义是：人们为了一个目标，人为地造成一个比较理想的环境，设法排除次要因素的干扰，努力减小实验误差，控制变量进行研究的活动。 A、正确 B、错误
