题目

下列转化不能一步完成的是（  ） A．CaO →CaCl2                      B．CaCO3 →Ca（OH）2 C．BaCl2 → Ba（NO3）2                      D．CuSO4→Cu(OH)2 答案：BTeachers should ___ their students to practice __ English as much as possible.A. encourage, speakingB. let, speakC. make, speak