题目

阅读理解 If you live in a big city, there are manythings to drive you crazy in your life. Vicky Zhao is a mainlander working inHong Kong. For her, one thing she can't put up with is people standing on thewrong side of the escalators in subway stations. Escalators help us movefaster and save time. It isn't a place to rest, the 24-year-oldmainlander says. I often see tourists block the way with their cases orchatting on the escalators during rush hour. It always annoys me. The logic（逻辑） behindthe stand right, walk left escalator etiquette seems obvious. Youshould leave enough space f鉴别一瓶气体是否为氧气，下列操作正确的是（ ）A．观察气体颜色B．闻气体的气味C．插入带火星的木条D．倒入澄清的石灰水