Quoting from above..

"You can connect to the database under certain single-user mode conditions by typing the command USE MSSQLSystemResource..."

So, the question should have named the database correctly as MSSQLSystemResource.

We all seem agree there is a hidden 'resource' which may or may not qualify as a database - my point earlier is that the question is vague\incorrect in the name.

Microsoft documentation refers to this as the resource database.

But, if the USE statement needs to have MSSQLSystemResource - then the database name is MSSQLSystemResource. The question is incorrect.

If USE Resource will never work. Then the question is incorrect.