He isn't at school. He ______________ be ill. [ ]
A. may
B. should
C. must
D. need
答案:A
可使心率加速,心肌收缩力增强的体液因素是()
A.乙酰胆碱
B.钾
C.镁
D.钠
E.心肌抑制因子
行车中当驾驶人意识到车辆爆胎时,应在控制住方向的情况下采取紧急制动,迫使车辆迅速停住。