简述顶板事故的预兆？
参考答案：
顶板事故的预兆有响声、掉碴、片帮、裂隙、漏顶、脱层。
The young woman ______ a important job in the company is from Canadian.[ ]
A. holds
B. held
C. holding
—Where are Maria and Kangkang?
—They _____ England.
A. had been in B. have gone to C. have been to
