8) these are the interactions in physical systems that do not appear to be reducible to more basic interactions. they include: gravitational, electromagnetic, strong nuclear, and weak nuclear

The fundamental forces or interactions is a term used in physics that explains the Forces that present in nature in their most basic form and cannot be further reduced.

Explanation:

The force of gravitation and the subatomic forces present inside the atom also known as some nuclear reactions and electromagnetic reaction are certain examples of fundamental forces.  all these forces are in their basic form of nature.

These  all make four such forces while another fifth force is a hypothetical one and is believed to be in existence hypothetically by the scientists.