1.Look at the boy and his dog___are coming this way.
C.that 只有that能同时指代人和物
2.Do you know the student__?
A.I often talk with 介宾
3.Afridge is a machine__ is used for keeping food fresh.
B.that 定语从句,that指代冰箱
4.John is the first boy__left the roo.
B.that 定语从句,因为之前有the first 修饰,所以不能用who