以下叙述中，不正确的是
A．催化剂在化学反应中能改变化学反应速率
B．氧气的化学性质很活泼
C．aL水和bL酒精混合后，总体积小于（a+b）L
D．混合物中一定含有两种或两种以上的物质
答案：B
解：A、催化剂是指在化学反应里能改变其它物质的化学反应速率，而本身的质量和化学性质在化学反应前后都没有发生变化的物质，所以正确．
B、空气的主要成分是氮气和氧气，常温下空气能稳定存在。所以B不正确．
C、由于分子间有间隙，水分子和酒精分子会进入对方的间隙中，故aL水和bL酒精混合后，总体积小于（a+b）L，所以正确．
D、混合物是指由多种物质组成的物质，其本质是物质的种类不是一种，混合物中一定含有两种或两种以上的物质，D正确．答案选B
| 阅读理解。 |
| Years ago,I lived in a building in a large city. The building next door was only a few feet away from mine. There was a woman who lived there and whom I had never met, yet I could see her sitting by her window each afternoon, sewing (缝纫) and reading. After several months had gone by, I began to notice that her window was dirty. Everything was unclear through the dirty window. I would say to myself, "Why doesn't that woman clean her window? It really looks terrible." One bright morning I decided to clean my flat,including cleaning the window. Late in the afternoon after I finished the cleaning, I sat down by the window with a cup of coffee for a rest. What a surprise! The woman sitting by her window was clearly seen. Her window was clean! Then it dawned on me. I had been criticizing (批评) her dirty window,but all the time I was watching hers through my own dirty window. That was quite an important lesson for me. How often had I looked at and criticized others through the dirty window of my heart, through my own shortcomings (缺点)? From then on, whenever I want to judge someone, I ask myself first, "Am I looking at him through my own dirty window?" Then I try to clean the window of my own world so that I can see others' world more clearly. |
| 1．The writer couldn't see anything early through the window because ______. |
[ ] |
| A．the woman's window was dirty B．his window was dirty C．the woman lived far away D．he was near-sighted (近视的) |
| 2．After the writer finished the cleaning he was surprised to find that ______. |
[ ] |
| A．the woman was sitting by her window B．the woman's window was still dirty C．the woman was cleaning her window D．the woman's window was clean |
| 3．The underlined part "it dawned on me" probably means "______". |
[ ] |
| A．I began to understand it B．it cheered me up C．I could see myself through the window D．it made me sad |
| 4．Which of the following is TRUE according to the passage? |
[ ] |
| A．Both the woman and the writer lived in a small town. B．The writer often cleaned the window. C．Both the woman and the writer worked as cleaners. D．The writer never met the woman. |
| 5．From the passage we can learn that ______. |
[ ] |
| A．one shouldn't criticize others very often B．one should often keep his windows clean C．one should judge himself before he judges others D．one should look at others through his dirty window |