8×17×125 =17×（8×125）运用了乘法[ ]
A．交换律
B．结合律
C．交换律和结合律
答案：C
一个圆的半径扩大3倍，它的面积就比原来多2倍．______．（判断对错）
Tom insisted _____ history instead of business at university, but his mother insisted that he _____ her advice. [ ]
A. on studying, take
B. to study, must take
C. on studying, took
D. in studying, should take
