问题
选择题
在下列实验中，盛氧气的集气瓶里应该预先装少量水或铺一层细砂的是（ ）
A．硫黄燃烧
B．铁丝燃烧
C．蜡烛燃烧
D．木炭燃烧
答案
物质在氧气中燃烧时，集气瓶内必须预先加入少量细砂或水的是铁丝，因为铁丝在氧气中燃烧火星四溅，生成灼热的四氧化三铁会溅落瓶底，从而使集气瓶炸裂．硫磺、蜡烛和木炭在氧气中燃烧都不会生成炸裂瓶底的物质．
故选B．
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在下列实验中，盛氧气的集气瓶里应该预先装少量水或铺一层细砂的是（ ）
A．硫黄燃烧
B．铁丝燃烧
C．蜡烛燃烧
D．木炭燃烧
物质在氧气中燃烧时，集气瓶内必须预先加入少量细砂或水的是铁丝，因为铁丝在氧气中燃烧火星四溅，生成灼热的四氧化三铁会溅落瓶底，从而使集气瓶炸裂．硫磺、蜡烛和木炭在氧气中燃烧都不会生成炸裂瓶底的物质．
故选B．
In the dining room of my grandfather’s house stood a massive grandfather clock. Meals in that dining room were a time for three 36 to become one. The table was always spread with 37 containing love as the main ingredient (成分). And that grandfather clock stood like an old family friend, watching over the 38 that was a part of our lives. As a child, the old clock fascinated me. I 39 and listened to it during meals. Even more wonderful to me was my grandfather’s ritual (老习惯). He wound (上发条) that clock with a(n) 40 key carefully each day. I remember watching 41 my grandfather took the key from his pocket and opened the hidden door in the clock. He inserted the key and wound — not too much, nor too 42 . He never let that clock wind down and 43 . He showed us grandchildren how to open the door and let us each take 44 winding the key. After my grandfather died, it was days after the funeral 45 I remembered the clock! The tears 46 freely when I entered the dining room. The clock stood there quiet. Some time later, my grandmother gave me the key. The old house was 47 . No laughter over the dinner table, no ticking or chiming of the 48 — all was still. I took the key in my shaking hand and 49 the clock door. All of a sudden, I was a 50 again, watching my grandfather with his silver-white hair and blue eyes. He was there, 51 at me, at the secret of the clock's magic, at the key that held so much power. I stood there, 52 in thought for a long time. Then slowly and 53 I inserted the key and wound the clock. It sprang to life. Tick-tock, tick-tock, life and chimes were breathed into the dining room, into the house and into my 54 . With the movement of the hands of the clock, my grandfather 55 again.
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