Which word shows the best meaning of the underlined word in this paragraph?

Brad's grandmother gave him a check in his birthday card. He had to take it to his family's bank to cash it. The teller had him endorse it by writing his name on the back because that would ratify that he was the person the check was intended for.

A.
finish

B.
spend

C.
authorize

D.
prepare

underlined word is endorse