The correct answers are B) credible. C) factual. D) secondary.
The descriptions that characterize this source are credible, factual, and secondary.
In this excerpt of "The First World War: A Complete History,"
Professor Martin Gilbert, Oxford University, 2014, the information attached is credible because it was researched by a renown historian, Professor Martin Gilbert. It is factual because he made his research and used appropriated sources, such as secondary sources to finish his work.