四级英语作文高级句型书信体介绍活动安排
AllNewtonhimselfhadsaid,whenhewaslostinthought,anapplefallingdowntohisthoughtofgravity.Newtonthenpointedoutthat,accordingtohislaw,gravitycausesthemoonalongtheellipticalorbitaroundtheearth,andtheearthandtheotherplanetsalongtheellipticalorbitrevolvearoundthesun.
