阅读下列短文，从每题所给的四个选项(A、B、C和D)中，选出最佳选项。A There are stock markets (股票市场) in large cities in many countries. Stock markets in Paris, London, Tokyo, Shanghai and New York are among the largest and most well-known. The stock, also called stock exchange, is a place where people can buy or sell shares of a factory or company. And each share means certain ownership of a factory or company. Different people go to stock markets. Some are rich, who want to get more money than they have. Others are not very rich, who buy stocks to try to become rich. Still others buy stocks as part of their plan to save money. Of course, investing (投资) money in the stock market is not the safest way to make money. No one can tell exactly whether the shares will be doing well. The factory or company may do badly. Then the stocks will go down, and the investors will lose money. The stock may go up or down for a number of untold reasons. Everyone wants the stock to go up, but sometimes even if a factory or company does a good job, the stock may still go down. No wonder going to the stock market is often compared to gambling (赌博). All are eager to make money by "gambling" in the stock market. Factories and companies that need money are pleased that so many people are willing to "gamble". Indeed, the stock market is an attractive and complex part of the business world. The passage mainly wants to tell us ______.

A. how to buy or sell shares
B. A B C of stock market
C. the stock market is like gambling
D. investing money in the stock market is not the safest way