Final answer:
a. Shelf space is the biggest constraint for traditional retailers, limiting the variety of goods that can be offered in physical stores compared to online retailers with more expansive storage in low-rent warehouses.
Step-by-step explanation:
For traditional retailers selling physical goods, a. shelf space is the biggest constraint limiting a firm's ability to offer customers what they want and when they want it.
Retail locations are often very expensive in terms of rent, which restricts the amount of physical product that can be displayed and stored.
This limitation means only a finite selection of goods can be offered at any given time, in contrast to online sellers like Amazon, who can offer a much broader selection due to their large warehouses in low-rent locations, achieving economies of scale.
Thus, shelf space in physical stores becomes a critical bottleneck, shaping the assortment of goods available for customers in traditional retail settings.