because是连词， "因为"，用来连接原因状语从句
I did it because he told me to (do it). 我做这事是因为他叫我做的。
Just because I don’t complain, people think I’m satisfied. 因为我没发牢骚，人们就以为我心满意足了
because of是介词短语，"因为(某人/某事物)；由于"，在句中作状语
They are here because of us. 他们是为了我们而来到这里的。
He walked slowly because of his bad leg. 他走得慢是因为腿有毛病。
