<prompt>  A patient presents with acute gastroenteritis in a dehydrated state. Which of the following conditions is highly suggestive of pre-renal renal failure?Urinary sodium 40 m mol; Urine osmolality 350m osmLUrinary sodium 40 m mol; Urine osmolality 500m osmLUrinary sodium 20 m mol; Urine osmolality 500m osmLUrinary sodium 20 m mol; Urine osmolality 350m osmL 