电泳涂潜用（）作为溶剂，避免了有机溶剂中毒和火灾的危险。
A.汽油
B.水
C.松节油
D.松香水
参考答案：B
频率大于______赫兹的声波叫做超声波．频率小于______赫兹的声波叫做次声波．
---Do you know when Dr Smith_____for dinner this evening?
----No,but I think he _____when he is free.
A．will come;comes
B．will come;will come
C．comes;comes
D．comes;will come
