knock,knock是一个笑话模式
The knock-knock joke is a type of joke, probably the best-known format of the pun, and is a time-honored "call and answer" exercise.
It is a role-play exercise, with a punster and a recipient of wit.
出处：
Knock, knock.
有人在家吗
Who's there?
是谁
Orange.
橘子
Orange who?
哪个橘子
Orange you going to give us a break... ...by zipping this credit card through the machine?
你是不是该通融一下用这台刷卡机呢

例如：
A:Knock knock.
B:Who's there?
A:Who.
B:Who who?
A:Are you owl?

语意表达：make an exception破格、例外
句型操练：Fine, I'll make an exception for you.
好吧，我为你破例一次。
Can't you just make an exception this one time?
你这次不能例外一次吗？
句型出处：I'm very sorry. I never do this, I'm asking you to make an exception in this one case.
抱歉…这是我第一次，能不能通融一次