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问题 多选题

两列平面简谐波以不同速度沿x方向传播，右图是 t=0 时刻这两列波在长a的区域内的波形．设 t=

4a
3v2
时刻该区域又一次出现相同的波形，则这两列波的速度 v1与v2的大小之比可能是（　　）

A．1：3

B．3：1

C．2：3

D．3：2

答案

由图象得知，两列波的波长分别为：

 λ1=a，λ2=

4
3
a

两列波的周期分别为：

T1=

λ1
v1
=
a
v1
，T2=
λ2
v2
=
4a
3v2

故t=T2=nT1，

由上得到

v1
v2
=
3n
4
（n=1，2，3…）

当n=4时，到

v1
v2
=
3
1
；当n=2时，
v1
v2
=
3
2
，由于n是整数，
v1
v2
不可能是
1
3
和
2
3
．

故选BD

单项选择题

Sometimes we have specific problems with our mother; sometimes, life with her can just be hard work. If there are difficulties in your (1) , it’s best to deal with them, (2) remember that any (3) should be done (4) person or by letter. The telephone is not a good (5) because it is too easy (6) either side to (7) the conversation.

Explain to her (8) you find difficult in your relationship and then (9) some new arrangements that you think would establish a (10) balance between you. Sometimes we hold (11) from establishing such boundaries because we are afraid that doing (12) implies we are (13) her. We need to remember that being (14) from our mother does not (15) mean that we no longer love her. If the conflict is (16) and you cannot find a way to (17) it, you might decide to give up your relationship with your mother for a while. Some of my patients had (18) "trial separations". The (19) allowed things to simmer down, enabling (20) .

5（）

A.innovation

B.manoeuvre

C.medium

D.synthesis
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单项选择题 A1/A2型题

颈部活动正常范围是（）

A.前屈60~80°；后伸35~45°；左右旋转各60~80°；左右侧屈各45°

B.前屈35~45°；后伸35~45°；左右旋转各60~80°；左右侧屈各45°

C.前屈35~45°；后伸35~45°；左右旋转各35~45°；左右侧屈各45°

D.前屈35~45°；后伸35~45°；左右旋转各60~80°；左右侧屈各80°

E.前屈35~45°；后伸35~45°；左右旋转各60~80°；左右侧屈各60°
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