A patient presents with acute gastroenteritis in a dehydrated state.Which of the following conditions is highly suggestive of pre-renal renal failure ?

• A. Urinary sodium >40 m mol; Urine osmolality < 350 m osm/L
• B. Urinary sodium >40 m mol; Urine osmolality < 500 m osm/L
• C. Urinary sodium >20 m mol; Urine osmolality < 500 m osm/L
• D. Urinary sodium >20 m mol; Urine osmolality < 350 m osm/L