Assets/FollowDestination.cs(6,13): error CS0246: The type or namespace name `NavMeshAgent' could not be found. Are you missing `UnityEngine.AI' using directive?的解决方案

using System.Collections;
using System.Collections.Generic;
using UnityEngine;


public class FollowDestination : MonoBehaviour {
    private NavMeshAgent ThisAgent = null;
    public Transform Destination = null;

    void Awake()
    {
        ThisAgent = GetComponent<NavMeshAgent>();
    }
    // Use this for initialization
    void Start () {
        
    }
    
    // Update is called once per frame
    void Update () {
        ThisAgent.SetDestination(Destination.position);
    }
}