void Select () {
   if(unitsSelected.Count > 0)
    ClearSelect ();  
   for(int i = 0; i < units.Count; i++)  
   {
    if(Mathf.Max(mouseWorldPoint1.x, mouseWorldPoint2.x) >= units[i].transform.position.x  
     && Mathf.Min(mouseWorldPoint1.x, mouseWorldPoint2.x) <= units[i].transform.position.x
     && Mathf.Max(mouseWorldPoint1.z, mouseWorldPoint2.z) >= units[i].transform.position.z  
     && Mathf.Min(mouseWorldPoint1.z, mouseWorldPoint2.z) <= units[i].transform.position.z)  
    {
     unitsSelected.Add(units[i]);
    }
   }
  }