题目内容：
根据下面材料，回答题：Today, many people are starving to death. There is a shortage of food and the available food is too expensive for hungry people to buy. Therefore, they go without food, or each day have only one or two small meals lacking the necessary vitamins to maintain good health.
Recently, a man who wanted to understand the conditions of such people conducted an experiment. He only ate one meal a day for a month but continued to work as he normally did.
During the first five days he was hungry at his regular meal times, but after he had drunk a glass of water his hunger went away. In the evening, when he ate his one meal, he ate quickly and consumed a large amount. During the next five days, although he was not hungry during the day, he quickly noticed every food stall. And the smell of food caught his attention. During the third and fourth weeks, he had hunger pains and lack physical strength. He looked forward to his one meal and ate it very slowly, enjoying every bite. Without it, he knew he would have hardly enough energy to work.
This experience changed his attitude about some things. Having a cup of tea was not just a pas-time, it also gave him strength. He more frequently noticed overweight people and people who threw away leftover food. He realized the importance of food for the very hungry person. He could no longer easily pass by a hungry beggar on the street. But most importandy, he could now sympathize in a small way with the starving people of the word.
According to the first paragraph, today the problem with many people is that_________ A．they don't eat food
B．they are too poor to buy food
C．the food they eat lacks vitamins
D．not enough food is provided to them
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