unity3d 在一个空心圆范围内随机生成物体

using UnityEngine;
using System.Collections;

public class RandomRadius : MonoBehaviour {
	public GameObject prefabs;
	// Use this for initialization
	void Start () {
		for (int i = 0; i < 1000; i++) {
			Vector2 p = Random.insideUnitCircle*3;
			Vector2 pos = p.normalized*(2+p.magnitude);
			Vector3 pos2 = new Vector3(pos.x,0,pos.y);
			Instantiate(prefabs,pos2,Quaternion.identity);
		}
	}
	
	// Update is called once per frame
	void Update () {
	
	}
}

只在红色区域内生成