烟中的尼古丁等有毒物质对吸烟者的呼吸、神经等系统都会造成极大的危害，而且还会对周围的人造成危害，可谓“害己又害人”．因此，我国采取了多种措施禁烟，自2011年5月1日起在公共场所全面禁烟，2015年又提高了烟草的税率，以期达到控烟的目的．尼古丁主要存在于烟草细胞的哪一结构中（　　）

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．