根据题目要求完成下列任务，用中文作答。

下面是某英语教师对学生作业的批改案例：

                                                                                            to hear

I think the most important sense is hearing.If I lose the ability of hearing,I also

cannot speak either                                  losing

can't speak. To lose( one's) hearing meansto lose two important functions( of human) .

                                                    an

Deaf-and-dumb people cannot hear the bus noise even if the accident happens in

behind them

their back. This is the most important problem for them. For example,suppose that

   are riding                                                                           danger

they ride a bike in the busy street. We,normal people feel the dangerous by the noise,which ismade by ears. We can avoid it and drive safely. Deaf people always expode their to danger.

                                                                                                                                                                                                                                  ? are always exposed to danger

根据所给信息完成下列任务：