单项选择题

A.水落口周围直径300mm范围内坡度不应小于3%
B.水落口周围直径300mm范围内坡度不应小于5%
C.水落口周围直径500mm范围内坡度不应小于3%
D.水落口周围直径500mm范围内坡度不应小于5%