Is your 3rd source a primary or secondary source?

Whether something is a primary or secondary source often depends upon the topic and its use.

A biology textbook would be considered a secondary source if in the field of biology, since it describes and interprets the science but makes no original contribution to it.

On the other hand, if the topic is science education and the history of textbooks, textbooks could be used a primary sources to look at how they have changed over time.

your answer will most likely be a.