什么叫点火提前角？点火过迟、点火过早有何危害？
参考答案：
点火提前角：从火塞发出电火花开始到活塞的达上止点为止，这个过程中曲轴所转过的角度称为点提前角。如果点火过迟，在活塞到达上止点时才点火，则混合气一面燃烧，活塞一面下行，即燃烧过程在容积增大的情况下进行，同时炽热的气体与气缸壁接触的面积增加，热传导损失增大，因而转变为有效功的热量相对减小。气体最高压力降低，从而导致发动机过热，功率下降。如果点火过早，由于混合的烯烧完全在压缩冲程进行，气缸内压力急剧升高，在活塞到达上止点之前即达到最大，使活塞受到反冲，阻止活塞继续向上运动，不仅使发动机的功率降低，并有可能引起爆震运动的零件和轴承加速损坏，甚至发动机报废。
下列获得氧气的方法中，不包含化学变化的是______
A．植物的光合作用 B．加热高锰酸钾 C．分解过氧化氢 D．分离液态空气．
阅读下面的文段，仿照画线句的句式，结合语境在横线处补写出恰当的句子。
我突然想到人的内心世界在审美上是多么神奇。你看遥远的东西是美丽的，因为它为人们留下了想象的空间，如悠悠的远山，如沉沉的夜空；朦胧的东西是美丽的，因为_____________，_____________，_____________。
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| It was a warm March evening, and I'd just taken a seat on the bus that would take me home. It was nearly 6:00 PM, but the bus was not yet full and the driver gave no 1 that he intended to start the bus. A middle-aged woman took a seat opposite me. She was crying. Not speaking to anyone in particular, she 2 narrated her story. She had come to the city to visit her daughter. On the way to the terminal, a thief had 3 one of her bags. It had contained half of the money she'd brought with her. The other half was hidden under her blouse, so she 4 still had some money left. The bus conductor, driver, and other passengers listened to her tale. At this time, an old man 5 got on the bus. He sat in the seat directly in front of the woman. After a few minutes, all seats were 6 . The driver got behind the wheel and started the engine. The bus conductor collected tickets and began asking us where we were 7 . When he came to the old man's seat, he became 8 and asked the old man Whether he had any money. The old man 9 that he did not. He explained that he 10 all his money this morning when he'd accidentally got on the wrong bus and now he was trying to go home. Upon heating this, the bus conductor 11 the old man to get off the bus. The old man was almost in tears as he begged the bus conductor to let him take that bus 12 he could get home before dark. The bus driver approached the old man, and repeated the conductor's 13 to get off the bus. "Stop troubling him! Can't you see he's only trying to get home?" she interfered. "He doesn't have any money!" the driver shouted. "Well, that's no 14 to throw him off the bus," she insisted. Then she said, "How much is his fare?" The bus conductor mumbled the amount. "Fine," said the woman. She 15 inside her blouse, took out her 16 money, and handed the fares to the bus conductor. "Here's his fare and mine. Just stop giving him a hard time." All eyes turned 17 the woman, who, just minutes before, had been crying over the money she'd lost. "It's only money," she shrugged. By the time the bus rolled out of the terminal, she had given the old man bread and a dollar. She rode the rest of the way home 18 a Mona Lisa smile of peace and grace, and the money she'd lost 19 was forgotten. On the road of life, the politeness and smiles of 20 can lighten our loads and lift our spirits. How much sweeter the journey when we make it a little smoother and richer for others! | ||||
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患儿乳食正常，体重增长正常，形体虚胖，太便每日4～5次，绿色稀便，伴有湿疹。应首先考虑的是（）。
A.大肠杆菌性肠炎
B.病毒性肠炎
C.金黄色葡萄球菌肠炎
D.真菌性肠炎
E.生理性腹泻
在ICD-10中，凡未提及病因的二尖瓣、主动脉瓣和肺动脉瓣的关闭不全，假定为（）。
A.风湿性
B.非风湿性
C.先天性
D.原发性
E.特发性
