
Explanation:

Box 1: No
The filtering is configured to synchronize Group2 and OU2 only. The effect of this is that only members of Group2 who are in OU2 will be synchronized.
User2 is in Group2. However, the User2 account object is in OU1 so User2 will not synchronize to Azure AD.
Box 2: Yes
Group2 is in OU2 so Group2 will synchronize to Azure AD. However, only members of the group who are in OU2 will synchronize. Members of Group2 who are in OU1 will not synchronize.
Box 3: Yes
User3 is in Group2 and in OU2. Therefore, User3 will synchronize to Azure AD.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-configure-filtering#group-b