两个物体相互接触,关于该接触处弹力和摩擦力,下列说法中错误的是( ) A.弹力和

题型:选择题

问题:

两个物体相互接触,关于该接触处弹力和摩擦力,下列说法中错误的是(  )

A.弹力和摩擦力都是接触力

B.有摩擦力必有弹力

C.如果有摩擦力,则其大小一定与弹力成正比

D.同一接触面上的弹力和摩擦力一定相互垂直

考点:弹力的产生、方向和种类滑动摩擦力、动摩擦因数
题型:选择题

—Dave, can you go to the zoo with us?

—Sorry, I can't. I have to ______. I don't feel well. [ ]

A. take a math lesson

B. babysit my sister

C. go to the movies

D. go to the doctor

题型:选择题

Once upon a time, there was a poor boy working for a king day and night, but the king treated him badly. Every day, the boy went cold and hungry, so he ran away. Then one day, he met a big lion in the desert. The lion looked angry and the boy was afraid. He was about to run away when the lion said, “I am angry because there is a thorn(刺) in my foot.” “Don’t worry. I will help you.” So the boy sat down and helped to pull the thorn out. From then on, they became good friends.

One day, the king went hunting in the desert and he caught the lion! He threw it into a net. On his way back he saw the boy and caught him as well. “I will punish you for running away. I will throw you to the lion’s den(兽窝)!” said the king angrily. So he did! But to the king’s surprise, when the lion saw the boy, it lay down and smiled. The boy smiled too and put his arm around his friend. Greatly moved, the king let the boy and the lion go.

小题1:Why did the boy run away from the king?(回答词数不超过8个)

小题2:What did the lion do when the boy was thrown to its den?(回答词数不超过8个)

小题3:What have you learnt from the story?(回答词数不超过12个)

题型:选择题

教育部提倡中小学生每天喝一杯牛奶或豆奶,主要是为青少年的生长发育补充哪种营养物质(  )

A.糖类

B.维生素

C.蛋白质

D.脂肪

题型:选择题

发生在口底正中线非牙源性发育性囊肿是()

A.鼻腭囊肿

B.甲状舌管囊肿

C.皮样囊肿

D.鳃裂囊肿

E.球上颌囊肿

题型:选择题

已知单相桥式整流、大电容滤波的直流电源,其输入交流电压为16V,则此电源输出的直流电压值为()。

A.18~20V

B.15~17V

C.<16V

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