There is no right answer.
User1 - Is already a quest user in fabrikan.com so they will not receive an OTP:
"Guest users who redeemed an invitation before email one-time passcode was enabled will continue to use their same authentication method."
User2 - This is an outlook account which is naturally seen as a Microsoft account without registering it as such. User will be prompted to just register with their Microsoft account and not have the option of OTP:
"Accounts such as an outlook.com, hotmail.com, live.com, or msn.com account, are managed by Microsoft, and therefore already considered Microsoft accounts."
User3 - this is just a normal user, not a quest user so they will not receive anything.
Source: https://learn.microsoft.com/en-us/entra/external-id/one-time-passcode
And a quick google search if outlook accounts are automatically Microsoft accounts which they are.
Correct answer:
E. None