1. Our sales have begun to fall off. 我们的销售额已经开始下降。
2. It's important to tighten up the wheels properly, otherwise they vibrate loose and fall off. 把车轮拧紧很重要,否则它们会振动而松脱。
3. In 'come back', 'break down' and 'fall off', 'back', 'down' and 'off' are all adverbial particles. 在come back、break down和fall off中,back、down和off都是副词小词。