What is the MAIN reason for having a developer sign a Non-Disclosure Agreement (NDA)?

A. Signing the NDA always gives consent to the developer to access tools and privileged company information to do their work.
B. Signing the NDA allows the developer to use their developed coding methods.
C. Signing the NDA protects confidential, technical, or Intellectual Property (IP) from disclosure to others.
D. Signing the NDA is legally binding for up to one year of employment.