问题
单项选择题
非正弦的周期交流信号可以用一系列（）表示。
A.正弦信号
B.和非正弦信号周期整数倍的正弦信号
C.和非正弦信号频率整数倍的正弦信号
D.和非正弦信号频率相同的正弦信号
答案
参考答案：C
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非正弦的周期交流信号可以用一系列（）表示。
A.正弦信号
B.和非正弦信号周期整数倍的正弦信号
C.和非正弦信号频率整数倍的正弦信号
D.和非正弦信号频率相同的正弦信号
参考答案：C
Directions: For each blank in the following passage there are four words or phrases marked A,B,C, and D. Fill in each blank with the word or phrase that best fits the context. When I was little, my family used to move frequently. Before I could even get acquainted with my schoolmates, my family was on the move again. I became very 36 because of this. But a girl with dark skin and ling shiny hair changed me. Here best characteristics are her openness and 37 . She is always smiling, like a beautiful sunflower following the sun. without doubt I enjoyed being with her and soon we became good friends. As time went by, I 38 became a happy girl. But this joyful period didn’t last long. We were admitted to different colleges. I felt like I had gone back to my always-on-the-move childhood. I felt 39 and helpless and I was afraid that I would 40 her as my best friend. She stayed calm and said to me :“Rain, you can achiever more than I do, so 1 to your dreams and make a big effort! Real friendship doesn’t fade and we will be best friends forever.” Maybe she didn’t realize what a great 42 she was to me at that time. However, it turned out that my concerns were well-founded（有根据的）. I felt that the 43 between us was getting bigger and bigger. One day, she sent me a text message happily telling me that she had fallen in love with a handsome boy in her class. I felt happy for her, but at the same time I was secretly worried about our friendship. I 44 her several times intending to tell her to think easefully about her relationship with the boy, but I got no more messages from her. I felt sad that perh  aps our friendship would not 45 . I had almost given up hope until she visited me at my campus a week later. She looked 46 but was wearing the most beautiful smile. She gave me a big hug and said: “I’m sorry. I want to be myself and your friend forever!” We cried together, ignoring the people walking past. She told me her sad story, and we knew we had gone back to how it was before.Now I firmly believer that distance and time can’t 47 you from a friend. If you care enough about each other, friendship never fades.
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