【单选题】听力原文: The United Nations refugee agency, UNHCR, says refugee protection is on the decline as countries harden their positions towards asylum seekers. Lisa Schlein in Geneva reports representatives fro...
A.
How to protect refugees effectively.
B.
How to protect national borders from illegal migrants.
C.
How to reconcile proper and effective protection for refugees with measures to control illegal migration.
【简答题】某小流域集水面积F=3km 2 ,干流长度L=2km,流域坡度J=0.033,产流参数μ=2.3mm/h,汇流参数m=0.70,暴雨衰减指搂n 1 =0.6(t<1h),n 2 =0.76(t≥1h),设计条件下雨力S p =103mm/h,试求设计洪峰流量。 (1)Q m 所取范围为90~100m 3 /s。 (2)Q m 试算误差要求在2%以内。 (3) ,t c <τ, ,t c ≥τ,