Every day, about one-quarter of American adults eat at fast-food restaurants. Cheap, tasty, and convenient, fast food is rich in fat and calories, and it's low in fiber and nutrients. Thanks in large part to fast food, half of America's adults and one-quarter of its children are fat, double the rate of a generation ago. In the past two decades, eating habits have changed as people pay more attention to their health. However, many Americans continue to eat red meat (beef in particular) as well as pork, chicken and other foods. Although beer and wine are popular in most areas, many Americans _ alcohol, because they think they will become healthier without drinking it. Various kinds of mineral water are commonly available. Eating styles and habits vary between people of different backgrounds, but Americans generally eat with the fork in the hand with which they write. A knife is used for cutting and spreading; otherwise, it is laid on the plate or table. Fast foods, such as chips, fried chicken, hamburgers, and pizza, tend to be eaten with the fingers. There is an obvious difference between what people may do at home or in a fast-food restaurant, and how they act in a more formal restaurant. Because both parents often work outside the home, some Americans are less likely to sit down as a family to eat once the children are older and able to prepare their own food or serve themselves. American have changed their eating habits in the past twenty years because   _  .
they want to keep healthy economy develops faster they have different backgrounds they have to work outside
Question: Every day, about one-quarter of American adults eat at fast-food restaurants. Cheap, tasty, and convenient, fast food is rich in fat and calories, and it's low in fiber and nutrients. Thanks in large part to fast food, half of America's adults and one-quarter of its children are fat, double the rate of a generation ago. In the past two decades, eating habits have changed as people pay more attention to their health. However, many Americans continue to eat red meat (beef in particular) as well as pork, chicken and other foods. Although beer and wine are popular in most areas, many Americans _ alcohol, because they think they will become healthier without drinking it. Various kinds of mineral water are commonly available. Eating styles and habits vary between people of different backgrounds, but Americans generally eat with the fork in the hand with which they write. A knife is used for cutting and spreading; otherwise, it is laid on the plate or table. Fast foods, such as chips, fried chicken, hamburgers, and pizza, tend to be eaten with the fingers. There is an obvious difference between what people may do at home or in a fast-food restaurant, and how they act in a more formal restaurant. Because both parents often work outside the home, some Americans are less likely to sit down as a family to eat once the children are older and able to prepare their own food or serve themselves. American have changed their eating habits in the past twenty years because   _  .
A. they want to keep healthy
B. economy develops faster
C. they have different backgrounds
D. they have to work outside
Answer: