问题
选择题
只用一种试剂或一种方法，经一步实验就可将O2，H2，CO2和空气四种气体区别开来的是
A．石灰水
B．带火星的木条
C．紫色石蕊试剂
D．燃着的木条
答案
答案：D
燃烧更旺的是氧气，有淡蓝色火焰的是氢气，木条熄灭的是二氧化碳，没变化的是空气
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只用一种试剂或一种方法，经一步实验就可将O2，H2，CO2和空气四种气体区别开来的是
A．石灰水
B．带火星的木条
C．紫色石蕊试剂
D．燃着的木条
答案：D
燃烧更旺的是氧气，有淡蓝色火焰的是氢气，木条熄灭的是二氧化碳，没变化的是空气
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| Soon it would be the holidays, but before that, there were year exams. All the 1 had been working hard for some time, reviewing their lessons for the exams. If they didn't 2 , they would have to retake them in September. There were usually a few who 3 , but Jane didn't want to be one of them. She had worked hard all year, 4 just before the exams she was working so hard that her sister Barbara was 5 about her. She went to bed too 6 . The night before the first exam, Barbara 7 that she have an early night and take a 8 pill. She promised to wake 9 up in the morning. As she was falling asleep, Jane was afraid that she might oversleep. Her 10 kept jumping from subject to subject. At last, with the help of 11 , she went to sleep. In no time at all, she was sitting in the examination hall, looking at the examination 12 , but she couldn't answer any of the questions. 13 around her was writing pages and gages. 14 she thought hard, she couldn't find anything to write 15 . She kept looking at her 16 . Time was running out. There was only an hour to go. She started one question, wrote two sentences, 17 and tried another one. With only half an hour left she wrote another two sentences. By this time she was so worried that she started 18 . Her whole body shook. It shook so much that she 19 up. She was still in bed and it had all been a 20 dream. A minute later, Barbara called her name. | ||||
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