Your network contains an Active Directory domain named contoso.com. You deploy Remote
Desktop Services (RDS) to four servers. The servers are configured as shown in the
following table.
You create a session collection named Collection1 that contains Server1 and Server2.
Collection1 will use user profile disks stored in a share named Share1. Two users named
User1 and User2 are members of a group named Group2. User1 and User2 will use RDS.
You need to identify which security principal must have full permissions to Share1. Which
security principal should you identify? To answer, select the appropriate object in the answer area.
Answer: 
Group 1 isn’t mentioned anywhere
Hmm, group 2 then?
No, group 2 is wrong. Each RD Session Host (and each RD Virtualization Host when using VDI) needs access to the profile disks share to be able to connect the user to the profile disk. With the question as stated above correct answer would be to select both server1 and server2.
I suppose one line is missing from the question this line would be like:
“Server1 and server2 are members of group1”
In that case the answer as given in the question is correct.