以下の文では、最後の文が未完成です。段落の下にリストされている4つの選択肢から、適切な文を選択してください。

Farmers in most of the industrialized countries grow cash crops today. This means that they usually grow and sell large amounts of only a few crops, such as soy, wheat, or corn. They use the money to buy what they need for their families and farms. In the past, farming was quite different. Most farmers used to grow many different kinds of crops and also raise cows, pigs, chickens, and other animals. They sometimes sold extra farm products or animals, but ●●●●.