As for food, after a lot of research it appears that sweet potatoes are the most calorie intensive crop that you can grow.

至于食物，经过大量研究表明，红薯是你能种植的热量最高的作物。

And the United States produced more than 80% of the world's cotton supply. Yet cotton was a very labor intensive crop which meant that human slavery remained crucial to the southern economy.

美国生产了80%的世界棉花供给然而棉花是种劳动密集型产业这意味着奴隶制对南方经济而言至关重要。