adjust 调节   例句：You can adjust your chair to make it more comfortable. 你可以调节一下椅子，使它更舒服一点。fall behind落后  例句： Students who are falling behind their peers at middle school may not necessarily lag behind them at college.在中学落后于同班同学的学生到了大学就不一定比其他同学差。What do you mean?你说的是什么意思？  对话：A: You'd better not buy this car.B: What do you mean?A: I mean it's too dear. 　A：你最好不要买这辆汽车。 B：你是什么意思。 A：我是说这辆车太贵了。