Final answer:
Crossbow limbs are initially straight and arc when strung, differentiating them from standard bows. Composite and crossbow limbs store mechanical energy to efficiently transfer to the arrow.
Step-by-step explanation:
While the passage you referred to mentions archers using composite bows capable of firing accurately at a range of four hundred feet, a crossbow operates on a different mechanical principle. Crossbows are distinguished from standard bows by their horizontal bow-like assembly mounted on a stock. Crossbow limbs are initially straight, but they do arc when the bow is strung. The string is drawn back mechanically, allowing the archer to aim without holding the tension. This mechanism gives the crossbow its unique ability to be held loaded and ready to fire for some time with minimal effort on the archer's part. The limbs of both crossbows and composite bows are constructed to store mechanical energy efficiently, which is then transferred to the arrow upon release.