“神舟八号”太空舱利用NiFe₂O₄将航天员呼出的二氧化碳转化为氧气，而  NiFe₂O₄   的质量和化学性质都不变。则 NiFe₂O₄在该过程中是（  ）

Service robot superstars shine at conference，aim to make life easier

    At the 2017 World Robot Conference, service robots were the stars．They work most closely with people．They help to do different jobs in daily life．

    Teotronice

    Teotronice is a music teacher．He looks like the famous ET, but his 53 fingers make him play the piano well．He played John Lennon's song Imagine at the conference．

    The supermarket robot

    Are you tired of shopping in the supermarket? Now，it becomes much easier with the help of the robot．You just talk to it，and then it will lead you to the things you need to buy．You can also use the robot to pay for your items．

    Bestic

    Bestic acts as a human arm to feed people with a spoon．This robot can be a good helper for kids，the elderly and those with difficulty using their hands．

“知了、知了…，”这是仲夏时节常常可以听到的声音．“蝉鸣林逾静，”在平常的日子里，知了那柔和的鸣叫声会使人心情格外平和，但今天不同，烈日当头，天气异常的炎热，知了发出的鸣叫声也异常的密集而响亮，令人心烦，是不是天气越热，鸣叫的知了越多呢？