滴眼剂有何种特点时，才能通透完整角膜
A．低浓度B．脂溶性C．水溶性和脂溶性D．低渗透压E．水溶性
参考答案：C
— Tom prefers ______ to ______.
— Let's ask him to take part in our dancing club. [ ]
A. to sing; dance
B. to dance; sing
C. singing; dancing
D. dancing; singing
安装三角架的膨胀螺栓不得少于（）颗。
A、2
B、4
C、6
