Reliable sources include so that readers can evaluate a source for themselves

D. citations.

Explanation:

The choices for this question are

A. correlations.

B. causations.

C. biases.

D. citations.

A reliable sources are those which provide a form to double check the information they are presenting, like an argument, a discussion, a well-reasoned theory, which are based on other true investigations. In other words, reliable sources provide citations and bibliography, through which you can check the information they are using to prove something.

Therefore, the right answer here is D. citations.

Additionally, if you observe other options, they don't offer reliability. For example, a source can offer correlation between events, but without citations and proves, that it's just a baseless theory.