The little boy, ________two attempts to climb over the fence of the garden, decided to have another try.[      ]

A. having made  

B. making

C. made  

D. has made

采用无油润滑往复式压缩机压缩天然气的原因之一是（）。

A.天然气易燃易爆

B.天然气析碳污染润滑油

C.天然气含水污染润滑油

D.天然气稀释润滑油