题目

First aid is a kind of help given to someone  61  falls ill or gets  62 (injure) before a doctor can  63  (find). First aid is  64  very important step in the  65   (treat).Now , let’s talk about first aid for burns . You can get burned by 66   (variety)things，  67   hot liquids , steam, fire , the sun and so on. Burns are called first , second and third degree burns , 68  (depend ) on which layers of the skin are burned . Different degree burn can be treated in a different way . 69 (keep) these things in mind will make a great 70  (different)        61._____将氮气、一氧化碳、二氧化碳的混合气体先通过足量澄清的石灰水、再通过足量灼热的氧化铜，最后剩余气体是（　　） A、氮气B、二氧化碳C、一氧化碳D、二氧化碳和氮气