简述桑代克尝试错误学习的基本规律。
参考答案：
(1)效果律；
(2)练习律；
(3)准备律。
The question that puzzles them is ___they can finish the work on time.
A．what it is that
B．what is it that
C．how is it that
D．how it is that
平面锉削的方法一般有三种（）、（）、（）。
