题干

在演示声音是由物体的振动发生的实验中,将正在发声的音叉紧靠悬线下的泡沫塑料球, 球被多次弹开。在此实验中,泡沫塑料球的作用是(   )

A:使音叉的振动尽快停下来

B:使音叉的振动时间延长

C:将音叉的微小振动放大,便于观察

D:使声波多次反射,形成回声

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答案(点此获取答案解析)

C

同类题5

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    It was a hot, humid day, and my brother Walt and I had decided that the only way to survive it would be to go swimming in a deep swimming hole across Mr. Blickez's pasture(牧场) and through some woods.

    The only problem with our plan was that this pasture was guarded by a huge, mean Hereford bull. Mr. Blickez had told us that Elsie was the meanest bull in the township, maybe even the county, and we believed him. But the hotter it got, the more we thought there was something fishy about his claim. For one thing, we remembered Mr. Blickez liked telling tall tales; for another, Elsie seemed like an odd name for a bull.

    Finally, I talked Mom into asking permission for us to walk through the pasture, but then another problem surfaced. Mom said she would talk to Mr. Blickez if we would take our cousin Joanie along with us. Joanie was almost two years older than me and a head taller. If her teasing ever got around my grade school, it would be all over for me. In fact, I still had a headache from a quarrel with her that morning. “I'm not going swimming with that dumb girl cousin.” I told my mom.

    “Either Joanie goes with, or you stay home alone,” Mom said in her serious tone. I gave in and we set out. On our way across the pasture, Walt yelled suddenly. Elsie had approached him quietly and was licking(舔) his back.Joanie and I dove under the wire fence, but while I was on the ground I looked up and saw that Elsie wasn't a big mean bull after all. She was going to keep licking my brother's back as long as he stood still.

    We had many good days growing up and visiting our secret swimming hole guarded by the so-called “big mean bull”. And as it turned out, for a girl cousin, Joanie hasn't been too bad. She's been one of my best friends over the years.