Why is earth's core mostly made of iron?
a. iron is radioactive.
b. iron is a very dense element.
c. iron is naturally hotter than other materials.
d. iron has a higher melting point than other substances.

This is because iron is a very dense element.

It is useful for historians to write narratives so that history can be passed on from their point of view.  think about a story being told in third person, then think about it again being told in first person, by someone who actually experienced the event.