I believe the correct answer is: A.) An article published in
a scientific journal.
Credible sources (or reliable) are scientific material that
are approved by the scholarly community, and are therefore regarded as
reliable. Materials such as articles, books, monographs, or research papers
that have been published in reputable peer-reviewed sources, or by
well-regarded academic presses, are credible sources that one can use in their
research to back up his/hers arguments. These materials can usually be found in
libraries, and sometimes on the Internet. Therefore, the credible source can be
found in a scientific journal, as it is approved by the scholarly community.
An article on Wikipedia describing the scientific method
cannot be regarded as credible source as anyone can change the
statements/facts.
A blog about the writer's own experiment cannot be credible
as it is a subjective and unapproved by other scientists.
An essay about science in a popular
magazine cannot be a credible source as it is published in popular magazine
and, therefore, not approved by scholarly community (as it is in scientific journal).
