In order for a research source to be useful, its author(s) must have (IB 3.3)a. Bias. b.Credentials. c.Refutations. d.Salaries.

credentials

Explanation:

In order for a research source to be useful, its author(s) must have credentials.

We should note that the credentials of an author has to do with the skills, information and the education that an author has that makes the author qualified to be able to elwrite on a particular topic.

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