任务型阅读。根据短文内容，回答下列问题。

Dear Zhang Qian,

Thanks for your letter. You want to know about my favorite sport and instrument(乐器). Now let me tell you. I like playing volleyball, basketball, and ping-pang. But swimming is my favorite sport. I am good at playing the violin and the guitar, too. My favorite instrument is the violin. I often play the violin on weekends. What about you? What’s your favorite sport? Do you like to play the violin or the guitar? Please write to me soon.     

Yours,

Li Ping

小题1:What’s Li Ping’s favorite sport?

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小题2:Is Li Ping good at playing the guitar?

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小题3:What does Li Ping often do on weekends?

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论述抖动产生的原理。