Which of the following was a major economic activity in the Middle Colonies?

The significant economic activity in the Middle Colonies was farming grains and cash crops. The region's climate and fertile soil made it ideal for agriculture, particularly the cultivation of wheat, barley, corn, and oats. These staples were not only crucial for local consumption but also for export, establishing the Middle Colonies as some of the leading producers of grain in the colonial economy.

In addition to grains, the Middle Colonies also engaged in the cultivation of cash crops, which included products like flax and hemp that were used in various industries. The agricultural abundance in this region contributed to its nickname, often referred to as the "Breadbasket Colonies" due to its role in producing food for both the colonies and Europe.

While mining for gold and silver was more associated with other regions like the Southern colonies, fishing and whaling were notable in New England, and manufacturing textiles primarily developed in the urban centers of the Northern colonies, none surpassed the prominence of grain farming in the Middle Colonies. This unique combination of favorable farming conditions and a focus on grain and cash crops defined the region's economy and set it apart from others during this period.