题干

关于电磁波,下列说法正确的是:

A:麦克斯韦在实验中发现了电磁波

B:变化的电场可以产生变化的磁场

C:雷达是用X光来测定物体位置的设备

D:使电磁波随各种信号而改变的技术叫做解调

上一题 下一题 0.0难度 选择题 更新时间:2018-03-15 03:20:43

答案(点此获取答案解析)

B

同类题2

     One afternoon I toured an art museum while waiting for my husband to finish a business meeting. I was looking forward to a quiet view (观察) of the art works.
     A young couple viewing the paintings ahead of me chatted non-stop between themselves. I watched them a moment and decided the wife was doing all the talk. I admired the husband's patience for putting up with her continuous talk. Distracted by their noise, I moved on.
I met with them several times as I moved through the different rooms of art. Each time I heard her constant burst of words, I moved away quickly.
     I was standing at the counter of the museum gift shop making a purchase when the couple came near to the exit. Before they left, the man reached into his pocket and pulled out a white object. He extended it into a long stick and then tapped his way into the coatroom to get his wife’s jacket.
    “He's a brave man.” The clerk at the counter said, “Most of us would give up if we were blinded at such a young age. During his recovery he made a promise that his life wouldn't change. So, as before, he and his wife come in whenever there's a new art show.”
“But what does he get out of the art?” I asked, “He can't see.”
    “Can't see? You're wrong. He sees a lot. More than you or I do.” The clerk said, “His wife describes each painting so he can see it in his head.”
     I learned something about patience, courage and love that day. I saw the patience of a young wife describing paintings to a person without sight and the courage of a husband who would not allow blindness to change his life. And I saw the love shared by two people as I watched this couple walk away hand in hand.
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