Your network contains an Active Directory domain. You have five organizational units (OUs)
named Finance, HR, Marketing, Sales, and Dev. You link a Group Policy object named
GPO1 to the domain as shown in the exhibit. (Click the Exhibit button.)

You need to ensure that GPO1 is applied to users in the Finance, HR, Marketing, and Sales
OUs.
The solution must prevent GPO1 from being applied to users in the Dev OU.
What should you do?

A.
Enforce GPO1.

B.
Modify the security settings of the Dev OU.

C.
Link GPO1 to the Finance OU.

D.
Modify the security settings of the Finance OU.

Explanation:

The OUs that are indicated by a blue exclamation mark in the console tree have blocked
inheritance. This means that GPO1 will not be applied to those OUs. For the Dev OU that’s
ok, but not for the Finance OU. So we have to link GPO1 to the Finance OU.

http://technet.microsoft.com/en-us/library/cc731076.aspx
Block Inheritance
You can block inheritance for a domain or organizational unit. Blocking inheritance prevents
Group Policy objects (GPOs) that are linked to higher sites, domains, or organizational units
from being automatically inherited by the child-level.
If a domain or OU is set to block inheritance, it will appear with a blue exclamation mark in
the console tree.