(1)I didn't buy it because it was too expensive.
(2)He is here because of you (that).
(3)He lost his job because of his age.
(4)We said nothing about it,because of his wife's being there.
(5)He knew she was crying because of what he had said.
(1)He didn't come because he was ill.
(2)He didn't come because of his illness.
(3)I can't stop fighting because I have a family.
(4)I can't stop fighting because of having a family.
(1)It is because he loves you.
(2)His absence was due to the rain.
(3)He was absent because of the rain.
有时若主语是代词(不是名词)，也可以用 because of引出的短语作表语。
(4)It is just because of money.
(5)That was because of his sickness.