what about 后应加doing 形式，故第一个空应为going即选Chike in the mountains 登山但是hike本意即为登山，后面的mountains有些多余，而且我觉得用in也不大合适。。But just in my opinion...
C.going;in
C
C.going;in what about 后加名词或动名词（即：动词ing）in the mountains
