折射仪可以测定宝石的轴性和光性。
参考答案：对
There are altogether eleven books on the shelf, ______five are mine.
A．on which
B．in which
C．of which
D．from which
对人体无害的气体有（）。
A.溶剂的烟气
B.一氧化碳
C.乙炔、丙烷
