becauseの品詞は？と聞かれて、そんな簡単なことを聞くな、conjunctionに決まってるだろ！と言われそうだが、ではbecause of のbecauseの品詞は何だ？
CambridgeのEngliah Grammar Todayによればbecause ofの２語でprepositionだ。conjunctionにofがくっついて品詞がprepositionに変わるのだ。
Because of is a two-word preposition meaning ‘as a result of’:
Because of the rain, the tennis match was stopped.
There were so many people in the shop because of the sale.