That做為關係代詞，不可用在非限制性定語從句中，即不可用在逗號後邊；定語從句中介詞之後也不可使用。在逗號或介詞後，指物時用which,指人時用who或whom。如下是小編給大家整理的用that寫定語從句三個，希望對大家有所作用。
例句 1）They arrived at a farmhouse, in front of ______sat a small boy.
A. whom B. who C. which D. that
解析：在介詞of之後指物，選擇C which。
例句 2）The engineer with _____my father works is about 50 years old.
A. whose B. who C. which D. whom
解析：選擇 D whom。介詞後指人。
例句 3）The letter is from my sister, ______is working in Beijing.
A. which B. that C. whom D. who
