If an announcement by a firm causes the price of that firm's stock to suddenly change, that price change will most likely be driven by:. a. the unexpected part of the announcement.
b. the expected part of the announcement
c. market inefficiency
d. systematic risk

The correct answer is the option A: The unexpected part of the announcement.

Explanation:

To begin with, the stock market is characterized for being completely umpredictable due to the fact that the information available for the common people is not enough to predict the possible behaviors of the prices, so that means that when an unexpected announcement happens and nobody new about it then the market will react depending on how it takes the new so that explains that if something not good happens all the sudden the priece of the stocks of that company will probably go down due to the bad reception of the news.