1. because of 是复合介词，其后可接名词或代词，动名词以及由关系代词型的所what 引导的从句等(但不能接that从句)。如：
He lost his job because of his age. 由于年龄关系他失去工作。
I said nothing about it, because of his wife’s being there.
He knew she was crying because of what he had said.
正：He cannot go to school because of sickness. / He cannot go to school because he is sick. 他因病不能上学。
误：He cannot go to school because of (that) he is sick.
2. 由because of 构成的介词短语一般只用作状语，而不用作表语。作表语时可用due to。如：
误：Tom’s absence was because of the rain.
正：Tom’s absence was due to the rain. 汤姆因下雨不能到场。
注：在阅读中有时也可见到because of 短语用作表语，但值得注意的是，此时句子的主语通常中代词而不是名词。如：
It is because of hard work. 那是因为劳累的原因。
That will be because of money. 那将是因为金钱的缘故。