无法隐式转换类型“UnityEngine”。Rigidbody2D到UnityEngine。Unity 2D内核中的刚体错误

我是Unity的新手 following a tutorial ,但当我编写代码时,我会收到以下错误:

无法隐式转换类型“UnityEngine”。Rigidbody2D到UnityEngine。刚性体'

代码:

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

public class PlayerCtrl : MonoBehaviour
{
    public float movSpeed;
    float speedX, speedY;
    Rigidbody rb;

    // Start is called before the first frame update
    void Start()
    {
        rb = GetComponent<Rigidbody2D>();
    }

    // Update is called once per frame
    void Update()
    {
        speedX = Input.GetAxisRaw("Horizontal") * movSpeed;
        speedY = Input.GetAxisRaw("Vertical") * movSpeed;
        rb.velocity = new Vector2(speedX, speedY);
    }
}

我该怎么解决这个问题? 我尝试调试和重写代码,但问题仍然存在。