请教android中怎么关闭一个指定的activity

请问android中如何关闭一个指定的activity
比如现在有N个activity a b c d ....
如果在d上关闭activity a

------解决方案--------------------
An activity can be shut down by calling its finish() method. One activity can shut down another activity (one it started with startActivityForResult()) by calling finishActivity().


在a里面设置一个静态的变量instance,初始化为this
在D里面,a.instance.finish()