这句话的意思是什么?

**The exchange requires certain strategies from its participants. An investor can buy stocks expecting increases or sell them anticipating possible declines**. When investors on the stock market are faced with a strong and prolonged increase in the price of securities, a bull market occurs. A bull in the stock market is therefore a person who is convinced that growth is about to happen.** Investors called bulls usually attack from the bottom up. In practice, this means that they buy more stocks and then wait for increases to sell them at a profit.** A bull market occurs when the prices of financial instruments increase by at least twenty percent. An experienced bull in the stock market will quickly notice her. **The stock market changes with certain mechanisms that advanced investors understand very well**. A bull market can occur in several markets. It includes securities as well as real estate and commodities.

Bear market is a term used in technical analysis to describe a situation in the financial market where asset prices are falling or have a downward trend. It is a period during which investors are pessimistic and expect further price declines.