Final answer:
The crop that became a dietary staple for Europeans after the Columbian Exchange was the potato (b). While maize (corn) also became significant, it was the adaptability and rapid growth of potatoes in Europe that made them especially integral to European diets.
Step-by-step explanation:
The New World crop that soon became a dietary staple for Europeans is potatoes (b). This is emphasized by the historical fact that after the Columbian Exchange, which involved the transfer of plants, animals, and diseases between the New World and the Old World, crops like maize (corn) and potatoes were introduced to the Old World. While maize also became central to many diets, it was the potato that became particularly significant in Europe, noted for its adaptability to the northern European climate and the fact that it could be easily farmed and grew rapidly. Both of these crops had a considerable impact on European agriculture and diets following their introduction after 1492.