42. 近年來文獻提出氣喘的死亡率已大幅降低，下列何者可能是降低氣喘死亡率最主要的因素？ (A) short- acting inhaled β 2 - adrenergic agonist做為氣喘急救用藥 (B) 併用short- acting inhaled β 2 - adrenergic agonist以及short- acting inhaled muscarine antagonist做為氣喘急救用藥 (C) inhaled corticosteroid (D) systemic corticosteroid