Which of the following is true about short-selling firms? 

a. A short-selling firm is a professional services firm that conducts in-house research to detect companies potentially committing fraud, enters into short-selling contracts relating to the stock of those companies, and then profits when investors react to their research and drive stock prices down. 

b. Short-selling firms helped bring to light frauds at Nikola and Luckin Coffee. 

c. Short-selling firms help to maintain the integrity of capital markets by providing information to users of the financial statements that would otherwise not be revealed in, for example, traditional securities filings made by companies to the SEC. 

d. All of the above. 

e. None of the above