探放小窑老空积水时，超前距离一般不得小于（）米。
A.10
B.20
C.30
D.40
参考答案：B
Bob often ____ bread for breakfast, but this morning he ____ some eggs. [ ]
A. has; had
B. had; had
C. has; has
D. had; has
轧制图表反映了轧制过程中（）的相互关系。
A．道次与时间
B．轧件与孔型
C．横梁与导卫
