1.选A fell off 是fall off的一般过去式 意思：跌倒,向下倾斜 ,强调的是“跌落、从……掉下来”,后直接接宾语.
The girl is falling off the bike.（= The girl is falling down from the bike.）
女孩正从自行车上摔下来.
They spread a big net in case Tom should fall off the tree and get hurt.
他们张开一张大网以防汤姆从树上掉下来受伤.
fall down 倒塌,掉下,不强调落物的来处
2.选C
get+sth.+done使某事被做 ,而这里的cut的被动形式还是cut,所以选C
You must get your homework done before you watch TV.你看电视前务必把家庭作业完成.
You'd better go and get your hair cut.你最好去理个发.