Amain sequence star becomes a after it uses up the hydrogen in its core.

Secondary star after it uses up the hydrogen in its core

Where are the statements so i can ?

Historians are researchers of the past or people who understand the history of people. with this field, they must possess qualities such as being unbiased, patient, efficient reader, has a knack for logic and critical thinking and reasoning, disciplined, open-minded, resourceful, with good analytical ability, good reasoning skills and problem solving!