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

答案b为什么不对呢？

B：leading to 55 percent more delay at airports and prompting.

OG说"55 percent more delay" is unclear。为什么呢？不明白