There are stock markets   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   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. Going to the stock market is often like gambling  . All want to make money by "gambling' in the stock market. Factories and companies that need money are pleased that so many people are ready to "gamble". Indeed, the stock market is an attractive  but part of the business world. The passage mainly wants to tell us   _   .
how to buy or sell shares the stock market is like gambling a general idea of stock market investing money in the stock market is not the safest way