问卷留置调查法属于（）
A、询问法
B、观察法
c、抽样调查法
D、全面调查法
E、实验法
参考答案：B
At present, we are studying a total of nine subjects, ________ I think is physics.
A．of them the most difficult
B．and the most difficult of which
C．the most difficult of them
D．the most difficult of which
属于升主动脉分支的是（）。
A.左、右冠状动脉
B.头臂干
C.右颈总动脉
D.右锁骨下动脉
E.胸主动脉
