根瘤土壤杆菌是著名的，因为它们能引起（）。 A.牙釉质腐蚀 B.湖干得快 C.植物疾

某校研究性学习小组的同学查阅化学史料时发现：

早在300多年前，英国化学家波义耳在一个敞口的容器中加热一种金属，结果发现反应后整个容器质量增加了，由此得出反应前后质量不守恒．之后，俄国化学家罗蒙诺索夫在密闭玻璃瓶内燃烧金属，发现反应前后整个容器质量不变，由此得出反应前后质量守恒．

这两位科学家的实验相似，为何结论不同？该学习小组沿着科学家的足迹进行实验探究，请你完成以下相关内容：

（1）提出问题：两位科学家得出不同的结论究竟与哪些实验因素有关？

（2）假设：若用同种金属、同一容器进行实验，两位科学家得出不同结论主要是由于______的缘故．

（3）实验验证：

已知：钠在空气中受热燃烧生成过氧化钠固体．

操作步骤及实验现象	简答
①在底部铺有细沙的锥形瓶中，放入一小块金属钠，塞紧橡皮塞，称量，用砝码使天平平衡．	称量前需要______
②取下锥形瓶，放在垫有石棉网的三脚架上微热，观察到金属钠着火燃烧，冷却后，再称量．	称量时观察到______
③将锥形瓶塞取出一会儿后，盖上瓶塞，再称量．	称量时观察到______

（4）得出结论：假设成立．

（5）交流与讨论：依据以上实验事实，解释两位科学家的实验结论：______

______．

（6）拓展与提高：小组内的同学又做了如下两个小实验．

①测定蜡烛燃烧前后的质量：实验前小组内同学推测蜡烛燃烧后质量会变轻，实验结果与推测一致．原因是生成的二氧化碳和水蒸汽扩散到空气中．请你接着分析，生成的二氧化碳和水蒸汽的总质量______（填“大于”、“等于”或“小于”）燃烧掉的蜡烛的质量，原因是______．

②测定镁条燃烧前后的质量：实验前小组内同学推测燃烧后生成物的质量比原来镁条的质量大，理由是______．但实际测定的结果却发现质量比原来镁条的质量减少了，请你帮他们分析可能的原因是______

______．

患者男，63岁，上颌全牙列缺失。下颌多数牙缺失，仅余左下7。牙槽嵴丰满，牙合间距离正常

患者反映戴义齿恶心，可能的原因是（）

A.后牙早接触

B.上颌后缘过长

C.义齿固位不好

D.后牙排列过于靠舌侧

E.以上都不是

同业拆借的特点包括（）。

A、期限短

B、金额大

C、风险低

D、手续简便

In modern society there is a great deal of argument about competition. Some value it highly, believing that it is responsible for social progress and prosperity, others say that competition is bad; that it sets one person against another; that it leads to unfriendly relationship between people.

I have taught many children who held the belief that their self – worth relied on how well they performed at tennis and other skills. For them, playing well and winning are often life – and – death affairs. In their single – minded pursuit (追求) of success, the development of many other human qualities is sadly forgotten.

　However, while some seem to be lost in the desire to succeed, others take an opposite attitude. In a culture which values only the winner and pays no attention to the ordinary players, they strongly blame competition. Among the most vocal are youngsters who have suffered under competitive pressures from their parents or society. Teaching these young people, I often observe in them a desire to fail. They seem to seek failure by not trying to win or achieve success. By not trying, they always have an excuse: “I may have lost, but it doesn’t matter because I really didn’t try.” What is not usually admitted by themselves is the belief that if they had really tried and lost, that would mean a lot. Such a loss would be a measure of their worth. Clearly, this belief is the same as that of the true competitors who try to prove themselves. Both are based on the mistaken belief that one’s self – respect relies on how well one performs in comparison with others. Both are afraid of not being valued. Only as this basic and often troublesome fear begins to dissolve (缓解) can we discover a new meaning in competition.

小题1:What does this passage mainly talk about?

A．Competition helps to set up self – respect.

B．Competition is harmful to personal quality development.

C．Opinions about competition are different among people.

D．Failures are necessary experiences in competition小题2:Why do some people favor competition according to the passage?

A．It improves personal abilities.

B．It builds up a sense of duty.

C．It pushes society forward.

D．It encourages individual efforts.小题3:The underlined phrase “the most vocal” in Paragraph 3 means ___________.

A．those who try their best to win

B．those who value competition most highly

C．those who rely on others most for success

D．those who are against competition most strongly.小题4:Which point of view may the author agree to?

A．Fear of failure should be removed in competition.

B．Competition should be encouraged.

C．Winning should be a life – and – death matter.

D．Every effort should be paid back.

机动车逃逸发生交通事故，保险公司是否应该赔偿?