题目

 “We’re in our new house. Let’s get a new pet to get along with us,” Mrs Brown said to her husband. “That sounds like a pretty good idea,” he answered. “Do you want to see the ads in the newspaper?” “Let’s go to the animal shelter. Many pets there need homes. Since tomorrow is Saturday, we can both go,” she said. Next morning the Browns met Mr Snow at the animal shelter. “We want to be sure that the pets here go to good homes,” Mr Snow said, “So I need to ask you some questions.” After they talked for a while, the Browns decided to get a small dog. It wouldn将充满NO2和O2的量筒倒立于盛有水的水槽中,经过一段时间后,水上升到量筒体积的一半处停止了,则剩余气体的成份是     A．O2                         B．NO                        C．NO2                       D．O2或NO