Which function should be used to return a date for calculating the difference?

The Directorof Marketing at Northern Trail Outfitters wants the app builder to create a formula field that tracks how many days have elapsed since a contact was sent a marketing communication. The director is only interested in whole units.

Which function should be used to return a date for calculating the difference?
A . DATFTIMEVALUE()
B. TODAY()
C. DATEVALUE()
D. NOW()

Answer: B