Willis环的组成包括（）
A.大脑前动脉
B.大脑中动脉
C.大脑后动脉
D.前交通动脉
E.后交通动脉
参考答案：A, B, C, D, E
We are earning more money. In fact most people are _____ than they were five years ago.[ ]
A. better off
B. well off
C. badly off
D. worse off
衡量润滑油性能指标中，闪点是保证机械设备不受腐蚀，也是控制润滑油精制深度的指标之一。
