Today our knowledge of food and what it does for bodies is far more advanced than that of the ancients. Now we know about vitamins and how each kind of vitamin helps in the growth of a special part of our body. There are on the market all kinds of vitamin pills which one can take to make up for one’s lack of certain important things which are needed for normal health. Of course, if we eat well and properly, the food that we eat will take care of our body without these pills so there is no need to take any kind of vitamin pills unless our doctor tells us that our bodies are short of something that can be supplied by them//Generally speaking, everything we eat does some good to our body, but if we eat too much of one kind of food and give not enough care to others, then we may be in trouble.//We are often told that we must eat more meat at each meal in order to get necessary proteins ( ). That is only partly true for proteins are not found only in meat. We can also get them from some vegetables such as the soybean. The soybean can be cooked in many ways and it is a great source of nutrition ( )//The best advice about what to eat is that we should eat all kinds of food but never too much of any. //( ) The main topic of the passage is ____.
选项：

A:food
B:vitamins
C:meat,
D:food