Science of the stars( 恒星科学 ) 2
The development of life( 生命的发展 )3 . Space travel and gravity( 太空旅行和重力 )功能Instructions( 指示 )语法Noun clauses as the subject( 主语从句 )重点单词astronomy , atmosphere , system , chain , theory , globe , violent , unlike , spaceship , oxygen , harmful , exist , presence , puzzle , gravity , satellite , climate ,crash , pull , float , mass重点短语in time , lay eggs , give birth to , in one's turn , prevent
from , block out , cheer up , now that , break out , watch out重点句型1
What it was to become was uncertain until between 4
5 and 3
8 billion years ago when the dust settled into a solid globe
2 . This produced a chain reaction , which made it possible for life to develop
3 .“ Oh dear ,” I cried ,“ walking does need a bit of practice now that gravity has changed