Velocity Player Movement

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

public class PlayerVelocityMovement : MonoBehaviour
{
    private Rigidbody rb2D;
    public float movementSpeed;

    void Start()
    {
        rb2D = GetComponent<Rigidbody>();
    }

    void Update()
    {
        //If "A" is being pressed...
        if(Input.GetKey(KeyCode.A))
        {
            //Applies velocity to -1 on the x axis, 0 on the y axis, and 0 on the z axis
            rb2D.velocity = new Vector3(-movementSpeed, 0, 0);
        }

        //If "D" is being pressed...
        if (Input.GetKey(KeyCode.D))
        {
            //Applies velocity to 1 on the x axis, 0 on the y axis, and 0 on the z axis
            rb2D.velocity = new Vector3(movementSpeed, 0, 0);
        }

        //If "S" is being pressed...
        if (Input.GetKey(KeyCode.S))
        {
            //Applies velocity to 0 on the x axis, 0 on the y axis, and -1 on the z axis
            rb2D.velocity = new Vector3(0, 0, -movementSpeed);
        }

        //If "W" is being pressed...
        if (Input.GetKey(KeyCode.W))
        {
            //Applies velocity to 0 on the x axis, 0 on the y axis, and 1 on the z axis
            rb2D.velocity = new Vector3(0, 0, movementSpeed);
        }

        //If "W" and "S" is not being pressed...
        if(!Input.GetKey(KeyCode.W) && !Input.GetKey(KeyCode.S))
        {
            //Get rid of any velocity on the z axis
            rb2D.velocity = new Vector3(rb2D.velocity.x, rb2D.velocity.y, 0);
        }

        //If "A" and "D" is not being pressed...
        if (!Input.GetKey(KeyCode.A) && !Input.GetKey(KeyCode.D))
        {
            //Get rid of any movement on the x axis
            rb2D.velocity = new Vector3(0, rb2D.velocity.y, rb2D.velocity.z);
        }

        //If "W" and "A" and "S" and "D" is not being pressed...
        if (!Input.GetKey(KeyCode.W) && !Input.GetKey(KeyCode.A) && !Input.GetKey(KeyCode.S) && !Input.GetKey(KeyCode.D))
        {
            //Sets velocity to 0
            rb2D.velocity = new Vector3(0, 0, 0);
        }
    }
}