限定用法與非限定用法

限定用法, 名詞後面直接加 who/which/that, 目的在於限制主詞在特定的條件下:

• The boys who are from XXX elementary school went to a picnic yesterday. (限制在那些來自某某國小的那群男孩)

非限定用法, who/which 前面加了 逗號(,), 目的在於增加資訊:

• The boys, who are from XXX elementary school, went to a picnic yesterday. (知道他們來自某某國小的資訊)