How does the modern study of history challenge earlier histories? a. by recognizing that they are not useful sources b. by categorizing them under a certain branch of history c. by questioning whether their sources are reliable d. by rewriting them using modern languages

The answer is C. By questioning whether their sources are reliable

Many sources of the past historical text was completely biased, depending on the writer's affiliation when writing the text.

For example, if we observe the text of European colonization in South East Asia that's written by a european writer, many of them filled by how their nations impose a fair trading agreement and treat the colony with respect and dignity.
If we observe the text that written by the colonized country, we will see that they feel they're being exploited and treated unfairly by the Europeans.