that指人时,相当于who或者whom；指物时,相当于which.在宾语从句中做主语或者宾语,做宾语时可省略.

　　(5)Thenumberofthepeoplethat/whocometovisitthecityeachyearrisesonemillion.

　　(6)Whereisthemanthat/whomIsawthismorning?

　　which指物,在定语从句中做主语或者宾语,做宾语时可省略

　　(1)Footballisagamewhichislikedbymostboys.

　　(2)Thisisthepen(which)heboughtyesterday.

　　when指时间,在定语从句中做时间状语

　　(1)IstillrememberthedaywhenIfirstcametotheschool.

　　(2)Thetimewhenwegottogetherfinallycame.

　　where指地点,在定语从句中做地点状语

　　(1)ShanghaiisthecitywhereIwasborn.

　　(2)ThehousewhereIlivedtenyearsagohasbeenpulleddown.

　　3.why指原因,在定语从句中做原因状语

　　(1)Pleasetellmethereasonwhyyoumissedtheplane.

　　(2)Idon’tknowthereasonwhyhelooksunhappytoday.