I made a text object in a script but Unity doesnt let me place the UI text in the box.

The Text object doesnt get placed in the Txt box in Destroy By Contact 21 Script.

NOTE: I am using Unity 5

Here is the C# script:

using UnityEngine; using UnityEngine.UI; using System.Collections;

public class DestroyByContact21 : MonoBehaviour {

 public GameObject explosion;
 public GameObject playerExplosion;
 public Text txt;

 private int currentscore=0;

 void Start () {
     txt = gameObject.GetComponent<Text>(); 
     txt.text="Score : " + currentscore;
 }
     
 void Update () {
     txt.text="Score : " + currentscore;  
     }

 void OnTriggerEnter (Collider other) 
 {
     if (other.gameObject.CompareTag ("Boundary")) 
     {
         return;
     };

     Instantiate (explosion, transform.position, transform.rotation);
     if (other.gameObject.CompareTag ("Player"))
     {
         Instantiate (playerExplosion, other.transform.position, other.transform.rotation);
     };

     Destroy (other.gameObject);
     Destroy (gameObject);
 }

}