A 70-year-old man enters the hospital emergency department and has been experiencing severe diarrhea（腹泻）. He has pallor, tachycardia, and an arterial pressure of 80/50, and has trouble walking. Which of the following therapies would the physician recommend to prevent shock? A: Infusion of a balanced electrolyte solution B: Blood infusion C: Administration of an antihistamine（抗组胺药） D: Infusion of a sympathomimetic drug （拟交感神经药）