​The information conveyed by changes in market prices is especially important in financial markets because

A) ​It forces individual investors to reveal their information about the prospects of a security
B) It assesses business decisions
C) It helps firms forecast the future demand for products
D) ​All of the above

Changes in market prices can indicate the sum of investors' opinions and beliefs about the future performance of a security or a product. This makes it necessary for individual investors to reveal their information, and helps firms forecast the future demand for products. It also assesses business decisions, such as the effectiveness of the management's decisions or the quality of a new product launch. Therefore, all of the above options are correct.