back door 字面意思就是这么简单“后门”，它可以指实实在在的后面的门，也可以是我们汉语中描述的“走关系的”后门，是一个非常好理解的习语，可以意为“走后门，走关系”，寓意：
to take indirect or unofficial route to get something done
采取间接的或非正式的方式来完成某事
to be dishonest in order to do something which is either of meaning or value
为了做有意义或有价值的事情而不诚实
也可以用 back-door，意为“后门的，不正当的”。
例如：
The agency was given to him because he slid into the contract through the back door.
因为他走后门签了合同，所以得到了代理权。
解析：because 引导的原因状语从句，用来说明对听众来说很重要的事情的原因。
She thinks that as long as the purpose is true, using the back door to achieve it is absolutely fine.
她认为只要目的是真的，走点关系来实现目标是绝对可以的。
解析：动名词 using the back door 作主语，谓语用单数 is.
The students could not be physically punished, but they were made to stand outside in the cold as a kind of punishment by the back door.
不能体罚学生，但可以走点关系，作为一种惩罚，让他们在寒冷中罚站。
解析：使役动词 make 在变被动语态时，要加不定式标识 to.
The data collection exercise was designed to open the back door to an energy consumption tax on home owners.
数据收集工作的目的是打开一个缺口向业主征收能源消费税。
解析：home owner 意为“业主”。
因为有了“后门”的存在，很多很顺理成章的事都变得崎岖坎坷，希望这个社会少点“后门”，多点公平，we don't act below the belt.
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