Section B
Directions: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice.
If you have gone on a diet and reached your goal, chances are good that when you stop dieting you will regain all the weight you lose. After several weeks on a low-calorie diet—900 calories or fewer— the body conserves energy by showing the speed at which it burns calories. This slow-down explains in part why your weight loss may cease after a few weeks. When you eventually return to eat a normal amount of food, your body may continue to burn calories at the slower rate, storing the remaining calories as fat. So if you are on a strict diet, your body may need fewer calories to maintain the same weight; losing weight becomes more difficult.
Doctors know that as you gain weight the fat cells in your body (most of us average 30 billion of them) become enlarged. But there is a limit to how big a fat cell can get, and very fat people develop additional fat cells—something more than 100 billion. It now appears that you can add fat cells at any point during your life, although the number you have is influenced by a combination of your history of dieting and your genetic makeup.
Fat cells differ distinctly from other cells in that they are made mostly of fat instead of protein and apparently they never go away, even after dieting. Instead, they merely shrink. Dr. Jukes Hirsch of Rckefeller University has examined the body tissue of very fat people who have lost weight, and found that it resembles that of starvation victims. Perhaps, he supposes, it is the billions of undersize, "hungry" cells that drive many formerly fat people off their diets.
New research reveals that your hungry cells aren't the only signal senders that tempt you toward the refrigerator. Another culprit may be the hormone insulin. Insulin tums sugar and fat into fuel for the body. In addition, some researchers believe that high levels of insulin are a factor in hunger and appetite—and may drive you to overeat.
Exercise helps maintain your weight and seems to bring insulin levels down, says Dr. Donald S. Robertson, a medical director. "Any weight -loss program must fail," he said, "unless it incorporates a certain amount of exercise."
When you stop dieting you will regain the weight you lost because ______.

A. the fat cells in your body have become enlarged
B. your appetite had become greater than before
C. your body can now consume only part of the calories you get from food
D. you have developed additional fat cells