A root account owner is trying to setup an additional level of security for all his IAM users. Which of the below mentioned
options is a recommended solution for the account owner?

A.
Enable access key and secret access key for all the IAM users

B.
Enable MFA for all IAM users

C.
Enable the password for all the IAM users

D.
Enable MFA for the root account

Explanation:
Multi-Factor Authentication adds an extra level of security for all the users. The user can enable MFA for all IAM users
which ensures that each user has to provide an extra six digit code for authentication.
http://docs.aws.amazon.com/IAM/latest/UserGuide/Using_ManagingMFA.html