20、One way to make an egg stand up is to break the thick end．This is an old way to fool others and Columbus once used that．Another way is to shake a fresh egg and hold it upright a few minutes so the yellow part of the egg will come down to the bottom．The yellow part of the egg is heavier than the white and will make the egg heavier at the bottom．You should be able to make it stand on its end（顶端）if you do everything tight．The third way is to place a little salt on a piece of white cloth before the test（试验）．The egg will stand in the salt，and your friends may think you are clever if they do not see the salt．

Fresh eggs will go down in water，If you find that an uncooked（生的）egg sits on water，you will know that it is made a long time ago，and has become bad．A fresh egg will not go down in salt water．Put in your fresh egg and watch it．

A magic can be played with a fresh egg，some salt and a glass full of water．First you fill the glass with some water，then put in two spoons of salt and move the spoon round and round until the salt is gone．Next you softly 6u fresh water in the glass．Please fill the water against the side of the glass so it will mix very little with salt water．It will not fall to the bottom because the salt is heavy，and it will not rise to the top through the fresh water，either．Your egg will stay in a place at the centre of the glass．

（    ）1．If you stand an egg on its end，it will _______

A．fall down             B．stand upright        C．fly                         D．be broken

（    ）2．If you shake a fresh egg long enough，the yellow part of the egg will _______．

A．become heavier      B．come to the bottom  C．come out               D．become light

（    ）3．A bad egg _______．

A．has no yellow part in it                             B．stays halfway in water

C．goes to the bottom in water                         D．can stay on water

（    ）4．Which is the best tide for the passage?

A．What are eggs?

B．A magic about eggs．

C．Tests on eggs．

D．The differences between fresh eggs and bad eggs．