The correct answer is:
a. A newspaper reporter who covered the Reagan presidency.
I believe a newspaper would be the most reliable source of information, because newspaper reporters tend to be subjected to higher standard of journalism. Even though it's true that bias would still exist depending on the journalist who wrote the coverages, they are the most trusted sources compared to other people in the options above.
The words that would best fit the given blanks in the sentence would be "slave traders" and "raw materials." The American and European colonisers are mainly dependent on the raw materials supplied by the slaves during the brink of the Industrial Revolution which gave these empires a huge economical boost.
