题干

小华在研究凸透镜成像规律时,将平行光正对凸透镜照射,另一侧的光屏移动到距凸透镜10厘米处时,得到一个最小最亮的光斑。接着把光源换成蜡烛,调整好相关器材的高度,将凸透镜固定在光具座中央50厘米刻度线处,移动蜡烛到光具座的左端并点燃,再移动光屏至如图所示位置时,在光屏中央得到一个清晰的像。保持凸透镜位置不变,通过移动蜡烛及光屏的位置,下列成像情况符合实际的是(    )

A:若蜡烛放置在10厘米刻度线处,移动光屏,在光屏上都不能呈清晰的像

B:若蜡烛放置在30厘米刻度线处,移动光屏,可在光屏上呈清晰缩小的像

C:若蜡烛放置在35厘米刻度线处,移动光屏,可在光屏上呈清晰放大的像

D:若蜡烛放置在45厘米刻度线处,移动光屏,可在光屏上呈清晰放大的像

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C

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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.