数值验证哈希中的值范围，得到该值在哪个key中

Setting[:elective_course] 输出：

{"优秀"=>{"start"=>85, "end"=>100, "score"=>5}, 
"良好"=>{"start"=>70, "end"=>84.9, "score"=>3}, 
"合格"=>{"start"=>60, "end"=>69.9, "score"=>2},
"不合格"=>{"start"=>0, "end"=>59.9, "score"=>1}}

判断90分在哪个hash中

Setting[:elective_course].select{|k, h| h["start"] < 90 && h["end"] >= 90}

输出：

{"优秀"=>{"start"=>85, "end"=>100, "score"=>5}}