Answer: C. Thursday, December 18th
Explanation:
The ex-date for dividends is the business day before the dividends are to be distributed. This is regardless of when the news of the dividends are announced by various entities.
The dividends are to be distributed on Friday, December 19th which means that the ex-date has to be the day before which is Thursday the 18th. As this is a weekday, we can assume that it is a business day as well.