Use the following information for questions 1 and 2. A 24-year-old female complained of weakness, tiredness, and shortness of breath on exertion. She has had recurrent black, tarry stools for about a month. Black tarry stools, or melena, indicate gastrointestinal bleeding. Her laboratory values are as follows: pH = 7.46, pCO2 = 25 mmHg, hemoglobin = 4.5 g/dL, [HCO3-] = 16 mM. What is the acid-base imbalance in this patient? Select one: a. metabolic acidosis. b. metabolic alkalosis. c. respiratory acidosis. d. respiratory alkalosis.