When you are learning to ride a bicycle,you often fall off. / 在你学骑自行车时，你常常会从车上摔下来。

比如说搜趣网
fall off the bike==fall down from the bike-----从自行车上摔下来
fall 搜趣网out (of)------从----中掉出：
A coin fell out of the envelope ------- 一只钱币从信封里掉了出来

fall off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.搜趣网）
女孩正从自行车上摔下来。
They spread a big net in case Tom should fall off the tr搜趣网ee and get hurt.
他们张开一张大网以防汤姆从树上掉下来受伤。