Answer: a. an abnormal price change immediately after the announcement
Step-by-step explanation:
In an efficient market, information is disseminated to participants at the same time which means that there isn't a chance for arbitrage. In such a market therefore, the prices of shares will reflect the information in the market.
In the above scenario, if the company shares such news, the share price of the company will react by changing in an abnormal way in other to match this unexpected news.