.if表示正面的条件，意为“如果”；unless意为“除非，如果不”=if...not
You will not be allowed to go into the room unless you show your ticket.
在时间和条件状语从句中，用一般现在时代替将来时。
We will have an outing if it is fine tomorrow.
until，连词，"直到"。常构成“not…until”结构，表示“直到…才”。
She didn't have dinner until she finished her homework.直到完成作业，她才吃饭。
although, even if，even though, as whether..or(not)可引导让步因状语从句。
although 不可与but 连用。
Although he was young, he faced the difficult situation calmly.