The correct answer is B because Cisco OSPF MD5 authentication on an interface requires two specific elements: enabling message-digest authentication and defining a message-digest key. On Cisco platforms, the correct syntax is:

ip ospf authentication message-digest

ip ospf message-digest-key < key-id > md5 < encryption-type > < password >

In this question, the engineer must use MD5 and store the password using 3DES encryption, which corresponds to encryption type 3 in Cisco syntax. Therefore, ip ospf message-digest-key 2 md5 3 P@ssw01 is the valid form. The key ID can be any matching integer on both neighbors, and here it is 2.

Option A is incorrect because authentication-key is used for simple password authentication, not MD5 message-digest authentication. Option C is incorrect because ip ospf authentication md5 is not the NX-OS/IOS syntax used here; Cisco uses authentication message-digest. Option D is invalid because authentication-key does not take md5 in that format.

So the issue is resolved only by enabling message-digest authentication and configuring the MD5 key with encryption type 3, which is exactly what B does.