关系代词有主格、宾格和属格（所有格）之分，并有指人与指物之分。that的用法最广，that 可指人也可指物。那么让我们来看一下英语关系代词常用that不用which的情况有哪些
1.先行词为不定代词all，little，few，much，anything，everything， nothing， something等时。
如：I will do all (that) I can to help you.我会尽力帮你的。
2.先行词被序数词、形容词最高级或the only, the very等所修饰或其本身就是序数词﹑形容词最高级时。
如：He was the only person that joined the army in his village that year.他是当年村里唯一参军的人。
3.先行词既有人，又有物时
如：They talked about the people and the things (that)they remembered in the school.他们谈论他们在学校里记得的人和事。
4.当主句是以who 或which开头的疑问句时，定语从句用that 引导，避免重复。
如：Who is the boy that was here just now?刚才在这里的那个男孩是谁？
