Geothermal corporation issued a press release before the stock market opened announcing that its earnings set a record for the highest ever. Explain how each of the following individual scenarios could be consistent with the semi-strong form of market efficiency.
(a) When trading opened after the announcement, the stock price quickly decreased by 20%.
(b) The stock price of Geothermal decreased slowly over the 30 days before the announcement that earnings were the highest ever.
(c) The stock price increased by 10% immediately following the announcement but then decreased throughout the day so that the closing price was only 2% above the previous day.
(d) The stock price of Geothermal did not change after the announcement was made public.