Final answer:
The bolded words in the sentence form an adjective clause, which provides additional information about the noun 'Books'. Option c.
Step-by-step explanation:
The question is asking to identify the type of clause represented by the bolded words in the sentence provided. In the sentence 'Books that deal with current events in an exciting way often become best sellers,' the bolded phrase is a dependent clause that modifies the noun 'Books' and thus is called an adjective clause.
It describes what kind of books often become best sellers by providing additional details about these books, specifically that they deal with current events in an exciting manner. An adjective clause typically serves to provide more information about a noun in a sentence, just like adjectives do.
So option c.