煤层顶板自上而下分为()。
A.老顶
B.直接顶
C.伪顶
D.破碎顶
参考答案:A, B, C
——Look at your pale face. You ______ a sleepless night.
——You bet. The work site next to the hotel was so noisy.
A.must have had
B.might have
C.should have had
D.cannot have had
循环母液在一次作业周期中所产生的氧化铝的克数,称为溶出率。