买来的新树脂往往是Na型或Cl型,新树脂使用前必须分别用酸(阳树脂),碱(阴树脂)浸泡约()个小时,把Na型或Cl型转换成H型或OH型。
A.3
B.4
C.5
D.6
参考答案:B
写出一个比5大的无理数 .
— Mr Wang, would you please tell me the result of the test?
— You've done a good job. You made _____ mistakes. [ ]
A. a few
B. few
C. a little
D. little