Sharing sets for internal users ?

Hi, there is this question in a certification quizz :

"The security model for Universal Containers is Private for the Case object.

When a support case is raised by a user with the Customer Community license, internal users are not able to see those Cases.

Internal users in the support role need to work on these Cases. How should internal users see these Cases?"

I answered with a sharing group (you create a sharing set for external users and then a sharing group for internal users)

(Sharing sets are for external users when you look at the help of Salesforce)

I am confused because I saw 2 quizz where the answer is : sharing set.

For me this is wrong (but if I must answer a wrong answer to get my certif,hum ..)

What do you think ?