How could the Marketing Cloud admin address this issue?

Northern Trail Outfitters’ employees are NOT receiving emails because the messages are being blocked by Spam filters.

How could the Marketing Cloud admin address this issue?
A . Import employee email addresses into All Subscribers with an "Active status
B . Ensure employees have opted in to the test email list or data extension
C . Ask employees to use personal email addresses instead of corporate email addresses
D . Provide the IT team a list of relevant IP Addresses to whitelist in their spam filter

Answer: D