对于因矿井防渗漏研究岩石渗透性，或者因含水层水位很深致使无法进行抽水试验的，可以进行（）。
参考答案：注水试验
— Liu Fang, I didn't know you can play the Pipa and Guzheng so well.
— Well, actually I ________ it since I was six years old. [ ]
A. plays
B. have been playing
C. played
D. had been playing
凸形竖曲线的最小长度和半径主要根据（）和（）来选取其中较大者
