放次放顶时期，直接顶冒落高度达不到采高（）倍时，则采用人工强制放顶。
A、2～3
B、2.5～3.5
C、1.5～2
D、1～1.5
参考答案：C
农村经济合作组织由哪些形式？
Hardly ____ into the country ____ it began to rain.
A． we had got; when
B．we got; than
C． had we got; when
D．did we get; than
