A、It may have a negative influence. B、It plays a very significant role. C、It is meaningless. D、It can have a positive impact. A

(16)It is what failed dieters have long suspected: Fat people really can’t keep the weight off. Scientists have confirmed that the majority of overweight people who try to lose weight either by cutting calories or exercising will return to their former size. Fewer than 10 percent of the 12 million Britons who go on a diet each year succeed in losing significant amounts of weight and most of those who do put it all back on again within a year. The scientists, from the Medical Research Council’s National Survey of Health and Development, followed 5 362 men and women from their birth in 1946 and 20 000 from birth in 1958, measuring their weight and blood pressure and assessing their lifestyles. They found both groups began gaining weight in the 1980s and had steadily increased in size ever since. Dr. Rebecca Hardy, the council’s program leader on body size, (17) said, "Once people become overweight, they continue relentlessly upwards. They hardly ever go back down. It is better to avoid getting fat in the first place. For men, weight goes up steadily through life. For women, it starts slowly and accelerates in the mid-thirties." Experts have suggested evolution means we are programmed to put on weight rather than lose it. (18) Dieting can make this tendency worse as decreasing calorie intake triggers the body to go into starvation mode and reduce the amount of energy it naturally expends, making it even harder to lose weight. But the study’s findings do not mean dieting is pointless, so eating less and taking more exercise can increase fitness and lower blood pressure.
16. What have the failed dieters suspected?
17. What do scientists find after the long-time observation?
18. What role does dieting play in losing weight according to the passage?