介词
介词是一种用来表示词与词, 词与句之间的关系的词。在句中不能单独作句子成分。介词后面一般有名词代词或相当于名词的其他词类，短语或从句作它的宾语。介词和它的宾语构成介词词组，在句中作状语，表语，补语或介词宾语。并且在定语从句“介词+whom/which”的结构中，不能用that 代替whom/which。She is a good student from whom we should learn.
I介词分类：
1 简单介词 about, across, after, against, among, around, at, below, beyond, during, in, on
2 合成介词 inside, into, onto, out of, outside, throughout, upon, within, without
3 短语介词 according to, because of, instead of, up to, due to, owing to, thanks to
4 分词转化成的介词 considering(就而论), including
5 形容词转化成的介词 like, unlike, near, next, opposite
