西机公司“应付账款—先锋公司”明细账3月末余额为（ ）元。
A．150000
B．54000
C．46000
D．24000
参考答案：D
As he _____ in the river for five hours, the thief looked very pale and hopeless.
A． trapped
B．has been trapped
C． trapping
D．had been trapped
血浆内下列哪一种阳离子浓度相对恒定是维持血容量恒定的关键（）。
A.K^+
B.Mg^2+
C.Mn^2+
D.Na++
E.Ca^2+
