What should you do first?

Your network contains two servers named Server1 and Server2 that run Windows Server 2008 R2.
Server1 and Server2 are configured as a failover cluster named Cluster1.
Cluster1 hosts a clustered application named App1.
App1 has a physical disk resource named Cluster Disk 1.
You need to use the Chkdsk tool to fix all of the errors on Cluster Disk 1.
What should you do first?

A.
From Disk Management, take Cluster Disk 1 offline.

B.
From Disk Management, disable write caching for Cluster Disk 1.

C.
From Failover Cluster Manager, modify the dependencies for Cluster Disk 1.

D.
From Failover Cluster Manager, enable maintenance mode for Cluster Disk 1.

Explanation:
Run a Disk Maintenance Tool Such as Chkdsk on a Clustered Disk
To run a disk maintenance tool such as Chkdsk on a disk or volume that is configured as part of a clustered service, application, or virtual machine, you must use maintenance mode. When maintenance mode is on, the disk maintenance tool can finish running without triggering a failover. If you have a disk witness, you cannot use maintenance mode for that disk.
Maintenance mode works somewhat differently on a volume in Cluster Shared Volumes than it does on other disks in cluster storage, as described in Additional considerations, later in this topic.
Membership in the local Administrators group, or equivalent, is the minimum required to complete this procedure
To run a disk maintenance tool such as Chkdsk on a clustered disk
1. In the Failover Cluster Manager snap-in, if the cluster is not displayed, in the console tree, right-click Failover Cluster Manager, click Manage a Cluster, and select or specify the cluster you want.
2. If the console tree is collapsed, expand the tree under the cluster that uses the disk on which you want run a disk maintenance tool.
3. In the console tree, click Storage.
4. In the center pane, click the disk on which you want to run the disk maintenance tool.
5. Under Actions, click More Actions, and then click the appropriate command:
* If the disk you clicked is under Cluster Shared Volumes and contains multiple volumes, click Maintenance, and then click the command for the appropriate volume. If prompted, confirm your action.
* If the disk you clicked is under Cluster Shared Volumes and contains one volume, click Maintenance, and then click Turn on maintenance mode for this volume. If prompted, confirm your action.
* If the disk you clicked is not under Cluster Shared Volumes, click Turn on maintenance mode for this disk.
6. Run the disk maintenance tool on the disk or volume.
When maintenance mode is on, the disk maintenance tool can finish running without triggering a failover.
7. When the disk maintenance tool finishes running, with the disk still selected, under Actions, click More Actions, and then click the appropriate command:
* If the disk you clicked is under Cluster Shared Volumes and contains multiple volumes, click Maintenance, and then click the command for the appropriate volume.
* If the disk you clicked is under Cluster Shared Volumes and contains one volume, click Maintenance, and then click Turn off maintenance mode for this volume.
* If the disk you clicked is not under Cluster Shared Volumes, click Turn off maintenance mode for this disk.
Source: http://technet.microsoft.com/en-us/library/cc772587.aspx