Answer:
c.it presented new keys to understanding Christianity
Explanation:
Calvin’s Institutes of the Christian Religion differ from the teachings of Luther because "it presented new keys to understanding Christianity."
This is evident in the fact that unlike Luther and most Christian doctrine at the time who believed in acquiring salvation through faith, John Calvin concluded that salvation is a matter of predestination and it's designed for some people only.
Hence, in this case, the correct answer is option C "it presented new keys to understanding Christianity."