The correct answer is alternative D) "By asserting that people could learn the truth themselves by reading and interpreting the Bible".
Individualism is a philosophical ideology that consists of the individual being independent and self-reliable. Self reliability and independence have everything to do with learning the truth by reading the Bible yourself.
Alternative D is the only alternative related to individualism, and for this reason, is the correct one.
Calvin didn't acknowledge the Pope as the head of the church.
Calvin believed that every individual was predestined to be saved or not, so alternative B is out of the question.
Calvin didn't think priests celebrating the sacraments was crucial.