爆破地点距老空（）m前，必须通过打探眼、探钻等有效措施，探明老空区的准确位置和范围、水、火、瓦斯等情况，必须根据探明的情况采取措施，进行处理。

A.10 

B.15 

C.20

^—The radio is too noisy and there is nothing interesting on it. Why don't you       ?

^—All right. I'll do that.[ ]

A. turn it on                        

B. turn it off

C. turn it back                      

D. turn it up