调类
参考答案：
就是声调的分类，是按照声调的实际读法归纳出来的，调值相同的归为一个调类。
— Robert is indeed a wise man.
— Oh, yes. How often I have regretted __________ his advice!
A．to take
B．taking
C．not to take
D．not taking
可锻性常用（）和（）来综合衡量。
