煤层顶板可分为那些？（）
A、伪顶
B、直接顶
C、基本顶
D、直接底
参考答案：A, B, C
—Look at the boy running on the ground . Is it David ?
—It be him. I saw him go to the teacher’s office just now. [ ]
A. must
B. mustn't
C. can't
D. might
第三方物流与传统的对外物流委托是同一概念。
