题目

—We didn’t find the Blacks _____ the lecture. —No one had told him about _____ a lecture the following day. (2006年苏州模拟题) A. to attend; there to be                     B. attend; there being C. attended; there be                     D. attending; there was   答案：B鉴别氢气、空气、二氧化碳三瓶气体，最简便的方法是（ ）A．分别通入紫色石蕊试液B．测定和比较三种气体的密度C．分别通入澄清石灰水D．用燃着木条分别伸入集气瓶内