问题 填空题

已知⊙O的半径为5厘米,若⊙O′与⊙O外切时,圆心距为7厘米,则⊙O′与⊙O内切时,圆心距为______厘米.

答案

设⊙O的半径为R厘米,⊙O′的半径为r厘米,则R=5厘米,

∵⊙O′与⊙O外切时,圆心距为7厘米,

∴R+r=7,

∴r=2,

∴当⊙O′与⊙O内切时,圆心距为R-r=5-2=3(厘米).

故答案为:3.

阅读理解

阅读理解.

     An old scientist recently made several tests with different animals to find out which was cleverer than

other animals.

     In one test the old scientist put a monkey in a room where there were several boxes. Some boxes

wereinside other boxes. One small box had some food in it. The scientist wanted to watch the monkey

and to find out how long it would take the monkey to find the food. The scientist left the room. He waited

a few minutes outside the door. Then he got down on his knees (膝盖) and put his eyes to the keyhole.

What did he see? To his surprise, he found himself looking into the eye of the monkey. The monkey was

on the other side of the door and looked at the scientist through the keyhole.

1. The scientist did the test to see _____.

    A. if the monkey would steal (偷) the food

    B. if the monkey would look for the food

    C. if the monkey was cleverer than other animals

    D. if some boxes were inside other boxes

2. In one test the scientist put a monkey _____.

    A. into a small box

    B. into several small boxes

    C. into a box where there was some food

    D. in a room

3. After the scientist left the room, the monkey _____.

    A. began to eat food

    B. began to look for food

    C. looked at the scientist through the keyhole

    D. came into the boxes one after another

4. The scientist _____.

    A. got down on his knees and waited outside the door

    B. got down on his knees and heard with his ears

    C. left the room for a long time

    D. looked at the monkey through the keyhole with his eyes

5. To the scientist's surprise _____.

    A. the monkey got down on its knees

    B. the monkey came out of the room

    C. the monkey looked at the scientist through the window

    D. the monkey put its eye to the keyhole

选择题