2016-2017学年 人教版 必修三 Unit 4 Astronomy :the science of the stars using language课件 (3)
2016-2017学年 人教版 必修三  Unit 4 Astronomy :the science of the stars using  language课件 (3)第2页

 A Visit to the Moon

1. gravity 2.gradually 3.float 4.mass 5.lessen 6.exhausting

by and by To be held up in air, gas or on the surface of liquid Quantity of matter, without regular shape; Tiring make or become less Force of attraction between any two objects,esp. that force which attracts objects towards the center of the earth.