题目

 The old pianist would’t listen to our repeated request that he _____ in public again.    A. was going to play     B. played                  C. would play                  D. play 答案：D为了除去NaCl晶体中混有的少量Na2CO3杂质（不得引入新杂质），可以在混合物中加入稍过量的 ，然后进行蒸发、结晶，即可得到纯净的NaCl晶体，有关化学方程式是 ．