Android : How do I make my button play a sound?

I know that this has been asked many, many times before, but how do I make my button play a sound when it's pressed?

this is my button's code:

 <Button
    android:id="@+id/c1"
    android:layout_width="250dp"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="45dp"
    android:background="@drawable/button_selector" />

and here is my MainActivity.java:

package com.example.appname;

import android.app.Activity;
import android.os.Bundle;

public class MainActivity extends Activity {
    /** Called when the activity is first created. */

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    }
}

what do I have to add to make my button play a sound? If it helps I'm using Eclipse.