What year were you born 与Which year were you born 的区别?

目前提问出生的大部分用When were you born?和Which year were you born?意思相同.都是问你哪年出生的.
如果用What year were you born 应该是问的生肖,用十二地支去回答.那用which的时候需要加上in吗不用加的。