once用於什麼時態

once作副詞意思是：曾經用於過去式。

例如：Once we were good friends.

once 作連詞時，可連接兩個句子，引導條件狀語從句，可用於一般現在時，也可用於一般過去時。例如：Once he makes up his mind ，nothing can not change it.

Once he made up his mind，nothing could not change it.