If it were not for oxygen and nitrogen in the air, no man could live on the earth. 大氣中如果沒(méi)有氧和氮，人就無(wú)法生存于地球了。
There are millions of living things on the earth. 世界上有數以百萬(wàn)計的生物。
Long ago enormous animals lived on the earth. 很久以前，地球上生活著(zhù)巨大的動(dòng)物。
Scientists have set up two kinds of relay stations. One kind is on the earth, the other is a satellite placed in space around the earth. 科學(xué)家們已建立了兩種中繼站，一種在地球上，而另一種是放在地球周?chē)罩械男l星上。
