阅读短文，回答问题。

     I am Wang Tao.  I am a student.  I study at Lianyi Primary School.  I often do my homework on

Friday evening.

     On Saturday, I go to see my grandparents by bike in the morning. They live in a small town near

my home, My grandfather likes fishing.  I like fishing but I don't know how.  In the afternoon my

grandfather and I go fishing. He teaches me carefully. Now I can fish, too. How happy I am!

     On Sunday morning, I often go to the park with my friends. Look! Yang Ling is playing on the

wings. Liu Tao and Wang Bing are playing on the slides. Gao Shan and I are catching insects.

     What a nice weekend ！   

1. Is Wang Tao a student?

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2. What does he often do on Friday evening?

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3. How does he go to his grandparents' home?

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4. Can Wang Tao fish now?

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5. What is Gao Shan doing in the park?

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（1）下列说法正确的是_____________。（填写选项前的字母）

（A）用透明的标准样板和单色光检查平面的平整度是利用了光的偏振

（B）如果做振动的质点所受的合外力总是指向平衡位置，质点的运动就是简谐运动

（C）变化的电场周围不一定产生变化的磁场

（D）狭义相对论认为：在惯性参照系中，光速与光源、观察者间的相对运动无关

（2）一列简谐横波沿x轴正方向传播，在t=0时刻的波形如图所示，波刚好传到x=3m处。此后x＝1m处的质点比x＝-1m处的质点_____________（选填“先” 、“后”或“同时”）到达波峰位置；若该波的波速为10m/s，经过时间，在x轴上-3m~3m区间内的波形与t=0时刻的正好相同，则=_____________。

（3）被称为“光纤之父”的华裔物理学家高锟，由于在光纤传输信息研究方面做出了巨大贡献，与两位美国科学家共获2009年诺贝尔物理学奖。光纤由内芯和外套两层组成。某光纤内芯的折射率为，外套的折射率为，其剖面如图所示。在该光纤内芯和外套分界面上发生全反射的临界角为60°，为保证从该光纤一端入射的光信号都不会通过外套“泄漏”出去，求内芯的折射率的最小值。