How can i return to specific previous activity on button pressed

Question

I have a next problem. Let's assume i have three Activities : A, B and C. I can come from A to C, and from B to C. Then when i pressed button in Activity C i want to go back to the previous Activity, or A or B. I don't know which one was previous.

in A Activity :

Intent intent=new Intent(this, C.class);
Intent.PutExtra("FROM_A", "A")
StartActivity;

in B Activity :

Intent intent=new Intent(this, C.class);
Intent.PutExtra("FROM_B", "B")
StartActivity;

in Activity C:

public void onClick(View v) {
    onBackPressed();    // automatic know which Activity i came from(A or B)
} 

Please Help Me. What's Wrong?

Thank you for your answers.

Answer 1

in Activity A :

    Intent intent=new Intent(this, C.class);
    intent.PutExtra("FROM_A", "A")
    startActivity(intent);
    finish();  

in Activity B :

    Intent intent=new Intent(this, C.class);
    intent.PutExtra("FROM_B", "B")
    startActivity(intent);
    finish();  

in Activity C:

    public void onClick(View v) {
      Intent intent=new Intent(this, YourActivity.class);
      startActivity(intent);
      finish();  
    }