问在Unity中找不到rigidBody2D.MovePosition

EN

using UnityEngine;
using System.Collections;

public class BasketController : MonoBehaviour {

    public Camera cam;
    // Use this for initialization
    void Start () {
        if (cam == null) 
        {
            cam = Camera.main;      
        }
    }

    // Update is called once physics TimeStep  
    void FixedUpdate () {
        Vector3 rawPosition = cam.ScreenToWorldPoint (Input.mousePosition);
        Vector3 targetPosition = new Vector3 (rawPosition.x, 0.0f, 0.0f);
        rigidbody2D.MovePosition (targetPosition);
    }
}

error CS1061: Type `UnityEngine.Rigidbody2D' does not contain a definition for `MovePosition' and no extension method `MovePosition' of type `UnityEngine.Rigidbody2D' could be found (are you missing a using directive or an assembly reference?)