题目

甲、乙两种物质间有如图所示的转化关系（“→”表示一步实现，部分物质和反应条件略去）。不符合上述要求的一组物质是（ ）A. NaOH、NaNO3 B. CO2、CaCO3 C. O2、H2O D. Fe、Fe3O4 答案：【答案】A【解析】A、钠盐、硝酸盐溶于水，所以硝酸钠不会转化成氢氧化钠，故A错误；B、二氧化碳和氢氧化钙反应会生成碳酸钙，碳酸钙高温会生成二氧化碳，可以相互转化，故B正确；C、氢气和氧气点燃生成水，水通电生成氢气和氧气，可以相互转化，故C正确；D、铁和氧气点燃生成四氧化三铁，27、During the day we work and play and at night we sleep. Our bodies rest while we sleep. In the morning we are ready to work and play again. It is while we are asleep that our bodies grow most. When children feel tired and angry, they usually need more sleep. We can get our lessons better, and we feel better, too, when we have had plenty of rest. Boys and girls, eight or nine years old, need ten hours of sleep every night. Our bodies need plenty of air when we sleep. If we do not get enough fresh air we wake up feeling tired. While in bed we must not cover our heads. If we do, our lungs （肺） will not get enough fresh air. If we open our windows at night we can have plenty of fresh air. Cool air is better than warm air. Boys and girls must get plenty of sleep if they want to grow and be strong. 1．Our bodies grow most while we are ________.     A．eating              B．playing              C．sleeping            D．exercising 2．Which is the best air for us?     A．Hot air.            B．Cool air.             C．Warm air.           D．Dry air. 3．What often makes us feel tired in the morning?     A．Too much air.                             B．Not enough fresh air.     C．Too much cold air.                         D．Too much sleep. 4．How can you get plenty of fresh air at night? You can______.     A．open your windows                        B．not sleep in bed     C．sleep ten hours                            D．go to bed late 5．The writer is trying to tell boys and girls ______.       A．to get their lessons better                     B．not to cover their heads C．how to go to bed                                          D．to get plenty of sleep