What Is the Most Important Difference Between a Corporate Bond

What is the most important difference between a corporate bond and an equivalent
Treasury bond?

A) Corporate bond payments are made by a check from the firm and Treasury bonds are paid by printing money by the government.
B) Corporate bonds are traded on the floor of New York Bond Market and Treasury bonds trade in the over-the-counter market.
C) In the case of the corporate bond, the firm has the option to default whereas the government supposedly doesn't.
D) None of the above.