粘结性好的煤，其结焦性一定好；结焦性好的煤，其粘结性不一定好。
参考答案：错
My father _____ to America. He _____ there three months ago. [ ]
A. went; has been
B. has been; has gone
C. has gone; went
D. has went; went
（）能够引起事故停车。
A、失火
B、仪表风中断
C、中压蒸汽中断
D、循环水中断
