金属、塑料门窗玻璃密封条安装不得有（）。
A、接缝
B、卷边、脱槽
C、滑动
参考答案：B
The research mainly deals with the difficulty the students have ________ their attention on their study all
the time.[ ]
A．to focus
B．to be focused
C．focusing
D．focused
下列哪种药物对肾脏毒性最大（）
A.青霉素G
B.阿莫西林
C.利福平
D.头孢孟多
E.环孢素
