Read this paragraph from The Dark Game. To assure that the intelligence reached the commanders as quickly as possible—the postal services having become slow and unreliable—Van Lew created a system of couriers that moved the intelligence on its way without burdening one operative with the responsibility (and danger) of making the entire trip. She also created a credible cover story for each of her couriers, should they be stopped and questioned along the way. The central idea of this paragraph is that