未焊透是指焊接时接头的（）未完全熔透。
A、坡口钝边和根部
B、中部
C、上部和根部
D、根部
参考答案：D
— Don't you know your computer has been infected with viruses?
— Really, no wonder it hasn't ________ as well as before. [ ]
A. appeared
B. operated
C. managed
D. controlled
反铲挖土机适用于（）。
A．停机面以上的Ⅰ～Ⅳ级土挖掘
B．停机面以下的Ⅰ～Ⅱ级土挖掘
C．水下挖掘
D．地下连续墙挖土
