【单选题】You must use heaters very carefully as they can easily ______ objects on fire if you are careless. [ ]
【单选题】You ______ use your mobile on the plane, but you ______ listen to music. [ ]
【单选题】-2.00+3.00×180镜片,表示平行光经镜片后,两条焦线在镜片( )。
【单选题】If you use your Telecard to make a local call you must ______.