定语从句分很多种情况的,先行词也就是根据具体的情况而定的.
“you are the only of the family who has received education”这句必须要用who的,因为who是修饰人的,that和which是形容物体的时候用的,而如果前面的先行词是比较级,或是像only这种词,必须要用that,不能用which代替.
“this is the only available address that there is life if you really want to contact him”,原理见上.