When triaging emergency room clients, which client should the nurse assess first?

B A female client with severe right lower abdominal pain who is febrile and vomiting. C An elderly client with peripheral vascular disease who is complaining of severe leg pain when ambulating. A A male adolescent who has been vomiting for the past 12 hours and describes himself as very weak. D A child who has had a cold for two days and now is coughing up green sputum.