题目内容

3.

A. She’s a student.
B. She’s is a secretary.
C. She’s an engineer.
D. She’s a teacher.

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4.

A.A list.
B.A product.
C.A contract.
D.A book.

5.

A.Where to have the meeting.
B.When to have the meeting.
C.Who to have the meeting.
D.What to discuss at the meeting.

如果一个振动的质点同时参与两个垂直方向,同频率的振动时,此质点的运动轨迹一般是椭圆

A. 对
B. 错

如果两个振动的的方向相互垂直,而且两个频率的比例为整数比,合成振动的轨迹是一系列平滑的曲线,这些曲线组成的图形叫李萨如图形.

A. 对
B. 错

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