android activity's intent and destroy, (between 3 activities) : I got three activities A, B ,C. A intent to B, B intent to C, when I finish the operation in C,I want to destroy C and straightly back to A, not B. 

I've tried "finish();B b = new B();b.finish()" in C, doesn't work; And "finish();B b = new B();b.onDestroy()" in C, And called a nullpointerException . 

So  how to achieve that