江西人教版选修六 第五单元P35 ,but this being my first experience

江西人教版选修六 第五单元P35 ,but this being my first experience
THe other two climbed down into the crater to collect some lava for later study,but this being my first experience,I stayed at the top and watched them.
but再接含逻辑主语的非谓语动词结构跟我以前学习的知识有冲突,
21.The secretary worked late into the night,___B__ a long speech for the president.
22.The secretary worked late into the night and __C___ a long speech for the president.
A.to prepare B.preparing C.prepared D.prepare
23.There _A__ some trouble over this in the past,I want to treat the matter carefully.
24.Because there _B__ some trouble over this in the past,I want to treat the matter carefully.
A.being B.was C.had been D.has been