When I click on Hands game object in the hierarchy in Unity, I don't see the option to assign the ThrowingObject script.

[SerializeField]
private GameObject throwingObject;

private Rigidbody objectRigidBody;

private Vector3 startingPosition;
private Quaternion startingRotation;

private float objectForce = 0f;
private float maximumForce = 600f;
private float delay = 1f;
private float timer;


// Use this for initialization
void Start () {

    objectRigidBody = throwingObject.GetComponent<Rigidbody> ();
    startingPosition = throwingObject.transform.localPosition;
    startingRotation = throwingObject.transform.localRotation;
    objectRigidBody.isKinematic = true;
}

// Update is called once per frame
void Update () {


    //If the player has started to click the mouse button...
    if (Input.GetMouseButtonDown(0)){

        BeginThrow ();
    }

    // If the player is continuing to hold down the mouse button..
    if (Input.GetMouseButton(0)){

        PowerUpThrow ();

    }


    // If the player releases the mouse button...
    if (Input.GetMouseButtonUp(0)){

        ReleaseObject ();

    }


}



private void BeginThrow () {

    // Reset Physics
    objectRigidBody.isKinematic = true;
    objectRigidBody.velocity = Vector3.zero;
    objectRigidBody.angularVelocity = Vector3.zero;

}


private void ReleaseObject() {

    //launch the object.
    object.RigidBody.isKinematic = false;
    throwingObject.transform.parent = null;
    objectRigidBody.AddRelativeForce (throwingObject.transform.forward * objectForce);

    // Reset the force and timer.
    objectForce = 0f;
    timer = 0f;
}


private void PowerUpThrow (){

    // Increment timer oncer per frame
    timer += Time.deltaTime;
    if (timer > delay)
        timer = delay;

    // Lerp the object force the longer the player holds down the button.
    float perc = timer / delay;
    objectForce = Mathf.Lerp (0f, maximumForce, perc);

}