A、B、C、D四家公司的风险管理效益比值分别如下，哪家公司的风险管理效果最好？（）
A．0．5
B．1
C．2
D．5
参考答案：D
x=0.8是方程x÷0.8=0.64的解．______．
Tom needs some help ________ his homework. Can you help ________? [ ]
A. to; he
B. with; him
C. to; him
D. with, his
