为什么用from whom ,只用whom为什么不对

为什么用from whom ,只用whom为什么不对
Daniel,we thought you were an adult,a person from whom we could expect good decisions

正常语序是
we could expect good decisions from a person
后面不缺主语和宾语,所以from不能省略
当然可以把from移到后面
Daniel,we thought you were an adult,a person whom we could expect good decisions from.
再问： 你好，请问你说的后面不缺主语和宾语是指哪个词后面，另外whom在此句中是做宾语修饰a person 吗
再答： whom引导的从句中不缺主语也不缺宾语 主语是we 宾语是good decision whom在从句中指代a person, from whom在从句中做宾语补足语