Answer:
D. Social engineering.
Explanation:
In IP spoofing, ip packets with a false ip address source is created with the sole intent on impersonating a client system in a network.
MAC (media access control) address spoofing is similar to ip spoofing, but is related to stealing MAC integrity to impersonate a system.
So, man in the middle security attack is very much related to an active member of a company planting security threat codes to gain access to restricted networks.
Social engineering clearly describes this scenario, as the culprit is not a member of company but played on the ignorance of a member.