英语顺口溜之that用法hat用法真有趣， 两个地方它不去; 逗号后边它不去， 介词之后不考虑; That做为关系代词，遥用在非遥遥定语从句中，即遥用在逗号后边;定语从句中介词之后也遥遥。
在逗号或介词后，指物时用which,指人时用who或whom。
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：在介词of之后指物，选择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：选择 D whom。
介词后指人。
例句 3)The letter is from my sister, ______is working in Beijing.
A.
which B.
that C.
whom D.
who 解析：选择 D who。
逗号后指人，在定语从句中做主语。