每分钟肾血流约占心排出量的（）.
A.1／2
B.1／3
C.1／4
D.1／5
E.1／6
参考答案：C
---____________the boy in a black coat ___________the UK ?
---No. He is ____________ U.S student .
A．Is… from , a
B．Does… come from , an
C．Is… come from , an
D．Is… from , an
提高铁路旅客服务工作水准的核心是（）
