3.
A. She’s a student.
B. She’s is a secretary.
C. She’s an engineer.
D. She’s a teacher.
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