i did as you said : 

public ActionResult Create()
        {
          

            var  items = _db.T_Materiel.Select(c).ToList<T_Materiel >;
            IEnumerable<SelectListItem> itemsSelect =new List<SelectListItem>
            foreach(var item in items)
            {itemsSelect.Add(new SelectListItem
                {
                 Value = c.Num_anael.ToString(),
                 Text =  c.Libelle
                });
            }

BUT : it says that it doesn't recognize "c"

and "foreach iz underligned" it says: "Une expression new exige que type soit suivi de (), [] ou {}" translation: "an expression new demand type to be followed by (), [] ou {}"

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