Inherance script problem [C#]

Hi everybody ! I have a problem with base script : i want to use it for differents types of turrets but i don't know how to solve problems : Instantiate, transform, startCoroutine and StopCoroutine are not recognized...

This is my two scripts :

BaseTower :

 using UnityEngine;
 using System.Collections;
 using System;
 
 public class BaseTower
 {
     private string towerName;
     private string towerDescription;
     private int towerPrice;
     private float towerDamage;
     private int towerRange;
 
 
     public string TowerName
     {
         get { return towerName; }
         set { towerName = value; }
     }
 
     public string TowerDescription
     {
         get { return towerDescription; }
         set { towerDescription = value; }
     }
 
     public int TowerPrice
     {
         get { return towerPrice; }
         set { towerPrice = value; }
     }
 
     public float TowerDamage
     {
         get { return towerDamage; }
         set { towerDamage = value; }
     }
 
     public int TowerRange
     {
         get { return towerRange; }
         set { towerRange = value; }
     }
 
 
     private GameObject mob;
     public GameObject bullet;
     public GameObject gun;
     public int power = 100;
 
     private bool isFiring;
     private IEnumerator fireRoutine;
 
     void Update()
     {
         if (mob != null)
         {
             transform.LookAt(mob.transform.position);
         }
     }
 
 
     void OnTriggerEnter(Collider col)
     {
         if (col.tag == "MobCol")
         {
             mob = col.gameObject;
             fireRoutine = FireRoutine();
             StartCoroutine(fireRoutine);
         }
     }
 
     void OnTriggerExit(Collider col)
     {
         // Make sure our initial mob should be removed
         if (col.gameObject == mob)
         {
             if (fireRoutine != null)
             {
                 StopCoroutine(fireRoutine);
             }
 
             mob = null;
         }
     }
 
     public IEnumerator FireRoutine()
     {
         // Use a Coroutine for this
         WaitForSeconds wait = new WaitForSeconds(0.2f);
 
         // Keep ourselves from firing at nothing
         while (mob != null)
         {
             Fire();
 
             // Return our yield instance
             yield return wait;
         }
     }
 
     public void Fire()
     {
         GameObject towerBullet = (GameObject)Instantiate(bullet, gun.transform.position, Quaternion.identity);
         towerBullet.GetComponent<Rigidbody>().AddForce(transform.forward * power);
     }
 }
 

and my tower script (not finished yet because i can't fix the first problem ) :

 using UnityEngine;
 using System.Collections;
 
 public class RifleTower : BaseTower {
 
     public RifleTower()
     {
         TowerName = "Rifle tower";
         TowerDescription = "Fast fire rate";
         TowerPrice = 100;
         TowerRange = 5;
         TowerDamage = 1f;
     }
 
 
 }
 

Thank you ! bye, xyHeat