北方屋顶变小甚至为平顶，而南方屋顶坡度大，影响因素是[ ]
A．降水
B．地形
C．风
D．太阳辐射
答案：A
If the threshold return is higher than the risk -free rate, what will be the relationship between Roy's safety -first ratio (SF) and Sharpe's ratio（）
A. The SF ratio will be lower.
B. The SF ratio will be higher.
C. They will be the same.
康复生物工程指矫形器和辅助具的应用，包括假肢、矫形器、助听器、导盲杖、各种辅助工具等特殊用具及轮椅等。（）
