OG-185：百分比的表示方法

185. The recent surge in the number of airplane flights has clogged the nation's air-traffic control system, to lead to 55 percent more delays at airports, and prompts fears among some officials that safety is being compromised.

(A)  to lead to 55 percent more delays at airports, and prompts

(B)  leading to 55 percent more delay at airports and prompting

(C)  to lead to a 55 percent increase in delay at airports and prompt

(D)  to lead to an increase of 55 percent in delays at airports, and prompted

(E)  leading to a 55-percent increase in delays at airports and prompting

我想请教的是：

（1）选项E中“55-percent"中的小横线是必须的吗？

（2）对于增加的百分率的表达方式，下列哪种是对的：

X rises 5% ；         X rises by a 5 %;

谢谢！