什么叫反馈？

John is twelve years old. He had a bad cold and coughed day and night. He went to see a doctor. The doctor gave him some cough medicine. Look at the instruction on the bottle of the medicine and then choose the right answers:

　　 Cough Medicine

　　Shake(摇动)it well before use.

Take it three times each day before meals.

　　Dose (药量):

　　Age：over 14 2 teaspoonfuls(勺)

　　8—13 1 teaspoonful

　　4—7 1／2 teaspoonful

Not right for children below the age of three. Put it in a cold place.

Use it before December 1st 2012.

小题1:John should take ____ a day.

A．2 teaspoonfuls

B．3 teaspoonfuls

C．4 teaspoonfuls

D．1 teaspoonful小题2:The medicine should be kept in _______.

A．a fridge（冰箱）

B．hot water

C．any place

D．the sun小题3: John should ____ before he takes it.

A．shake the medicine well

B．eat nothing

C．do some exercise

D．drink a cup of tea小题4: When people are ____ years old, they cannot take this medicine.

A．eighty

B．thirty

C．two

D．twelve小题5:John will ____ the medicine when it is left after Dec.1st, 2012.

A．throw（扔） away

B．stop to take

C．take once

D．take six times more

一列简谐横波沿x轴的正方向传播，在t=0时刻的波形如图所示，恰好传播到x=4m处．t=0.3s时，质点a第一次达到波峰位置，则该波的传播速度为______m/s；t=______s时，位于x=8m的质点b恰好第二次沿y轴负方向通过平衡位置．

属于三环类抗抑郁药是

A．米帕明

B．马普替林

C．碳酸锂

D．氟哌啶醇

E．氯丙嗪

在E-R图中，用来表示实体的图形是______。

A．矩形

B．椭圆形

C．菱形

D．三角形

属于委托人在代理合同中的义务的是( )。

A．承担赔偿损失的义务
B．向被代理人报告处理事务情况的义务
C．按照指示处理事务的义务
D．亲自处理事务的义务