4. The post-earnings announcement drift (PEAD) refers to a phenomenon that stock prices show positive (negativ drifts for a few months after positive (negative) earnings announcements. If we frequently observe PEADsn stock market, we would be able to reject a. only the wake-form efficient market hypothesis. b. only the semi-strong form efficient market hypothesis. c. both the semi-strong form and the strong-form efficient market hypotheses. d. only the strong-form efficient market hypothesis. e. None of the above options is correct