Aset of ideas about fundamental truths is called

a philosophical system
an abstract idea
an association
a symbol

In my opinion, the correct answer is A. a philosophical system.

If it is a set of ideas, it means it is organized, well established, and worked out to the last detail. On the other hand, "fundamental truths" are core truths, those that form the basis for many other truths. All the other options (an abstract idea, an association, a symbol) are singular and particular. They can be elements within a set of fundamental ideas.