题目

空气与人体呼出气体比较，下列叙述正确的是（ ） A．空气中氧气含量比呼出气体中多 B．空气中二氧化碳含量比呼出气体中多 C．空气中水蒸气含量比呼出气体中多 D．空气中氧气、二氧化碳、水蒸气含量都比呼出气体中多 答案：【考点】吸入空气与呼出气体的比较． 【专题】空气与水． 【分析】人呼吸时把空气中的氧气转化为二氧化碳，同时从体内带出水蒸汽，人体呼出气体和空气中的氧气、二氧化碳、水蒸汽含量不同，呼出的气体与吸入空气相比，具有“两多一少”的特点，据此分析解答即可． 【解答】解：人呼吸时把27、We are in a world full of competition．Our parents compete（竞争）with others in their offices，our brothers and sisters compete with others in their colleges，and we compete with our classmates in school．Many of us give up in the face of competition and will never be successful．①can't，others，why，we，do，better，than One important reason is that we have no self-confidence（自信）． In fact，everyone is born equal．You can do what others do．Although your classmates may be better than you in some ways，you may be better than them in other subjects．So everyone has his or her own advantages．Don't look at things from a single（单个的）point of view．Try to discover your own advantages，and believe that you can do better than others in those ways． Competition is not so terrible．Don't be afraid of it．And don't be afraid of those classmates who are better than you．②Remember that self-confidence is the first step to success．Believe in yourselves，and you will be successful one day． 1．Are we living in a world full of competition? 2．How can you improve your serf-confidence according to the passage? 3．将①处划线部分单词连成一个完整的特殊疑问句。 4．将②处划线部分译成中文。 5．What's the main idea of this passage?