Please make a mark ________ you have made a mistake.

1.答案：A.
2.翻译：请在你犯错误的地方做一个记号/标记.
3.
1）此为where引导的地点状语从句.
where为连词,可以翻译为“在...的地方”.
如：Where there is a river,there is a city.
在有河流的地方,就有一座城市.
2）如果选B,理解成which引导定语从句的话,则主句Please make a mark in都不完整；
如果理解成which引导宾语从句（做in的宾语）的话,则宾语从句you have made a mistake并不缺少which这个成分.
3）如果用C that的话,理解成宾语从句则主句Please make a mark不缺少什么宾语,倒是缺个地点状语；理解成定语从句,则关系代词that只能在定语从句you have made a mistake中充当名词性成分如主语/宾语等,但是同样这个定语从句并不缺少名词性成分.
4）如果选D the place where的话,后面的定语从句where you have made a mistake没有问题,where充当该从句的地点状语,但是很明显主句Please make a mark the place错误,因为the place不能单独在该句中充当地点状语,除非是Please make a mark at the place还差不多.
4.综上所述,正确答案为A.