How should the data be updated?

A company has one million subscribers. The company has a Master data extension that contains information about its subscribers, such as Email Address, Physical Mailing Address, Phone Number, and Loyalty information. There are 40 fields in the data extension. The data is used for multiple daily email campaigns.

How should the data be updated?
A . A file drop automation to execute an import every time a record is updated or added.
B . A scheduled automation to import a file containing all of their subscribers.
C . A scheduled automation to import a nightly file of updated or changed records.
D . A scheduled automation to occur every 15 minutes to ensure the data is current.

Answer: C