FlyingFred/Assets/Obstacle.cs

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

public class Obstacle : MonoBehaviour
{
    public List<GameObject> obstacleObjs;
    private void Start()
    {
        Starter();
    }
    void Starter()
    {
        int rand=Random.Range(0, obstacleObjs.Count);
        obstacleObjs[rand].gameObject.SetActive(true); 
    }
}