The ______meter can detect even a very small amount of gas in the room.

单项选择题A．Hello This is Tom Brown.B．Sure. Here you are.C．Sorry. The line is engaged.D．John Smith’s office. What can I do for you

单项选择题A．He’s tired.B．He lost the race.C．He has already been to the top of the hill.D．He prefers doing exercise indoors.