什么是水平移动系数?
参考答案:
在充分采动或接近充分采动的条件下,沉煤层走向的最大水平移动与地表最大下沉之比。
Mr Smith __________in London for a few years before he _____to China.
A.lives; came
B.has lived; came
C.had lived; comes
D.had lived; came