向Ba(OH)₂溶液中逐滴滴入稀硫酸，下列溶液的导电能力描述正确的是(    )

A．开始时导电能力肯定最强

B．当沉淀为最大值时，导电性最弱

C．先变强，后变弱

D．逐渐变弱

The ______ way is based on the premise that the teacher should be silent as much as possible in the classroom and the learner should be encouraged to produce as much language as possible.