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【简答题】
为测定空气中氧气的含量，某兴趣小组的同学选用了40mL的试管作反应容器（如图）和量程体积足够大且润滑效果很好的针筒注射器，将足量的白磷放入试管后，用橡皮塞塞紧试管，并夹紧弹簧夹。用酒精灯加热白磷，燃烧结束后，等到试管冷却后松开弹簧夹，观察现象。 （1）正式开始实验前，该兴趣小组同学打开弹簧夹，将注射器活塞从20ml刻度处推至15ml处，然后松开活塞，观察到活塞返回至20ml刻度处。该操作的主要目的是_________。 （2）实验后，可以观察到针筒活塞会从原来的20mL刻度处慢慢向左移到约_________处。 A．4mL刻度 B．8mL刻度 C． 12mL刻度 D． 16mL刻度 （3）下列实验操作，对实验结果有影响的是___________（填序号） A．装置有点漏气 B．白磷的量不足 C．用干燥的红磷代替白磷做实验
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【单选题】Which of the following statements is true about the Russian poet Pushkin?
A.
He said that inspiration only comes from geometry and poetry.
B.
He thought that testing is important for inspiration.
C.
He said that an important aspect for learning is inspiration or being inspired.
D.
He got upset about tests at school.
【单选题】Which of the following statements is true about the Russian poet Pushkin?
A.
He said that inspiration only comes from geometry and poetry.
B.
He thought that testing is important for inspiration.
C.
He said that an important aspect of learning any subject is inspiration or being inspired.
D.
He got upset about tests at school.
【简答题】轴承的组配方式有—、—、—.
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