1.常用that 不用which的情況:1）先行詞為不定代詞all,little,few,much, anything, everything, nothing, something等時.I will do all (that) I can to help you.2）先行詞被序數(shù)詞、形容詞最高級或the only, the very等所修飾或其本身就是序數(shù)詞﹑形容詞最高級時.He was the only person that joined the army in his village that year.3）先行詞既有人,又有物時They talked about the people and the things (that)they remembered in the school.4）當主句是以who 或which開頭的疑問句時, 定語從句用that 引導, 以避免重復.Who is the boy that was here just now?