A vSphere content library administrator is attempting to unpublish the content library, but the option is grayed out as shown in the Exhibit.

Which statement identifies the reason for not being able to unpublish?

A. Underlying storage for this content library is not accessible.

B. A synchronization operation is in progress with this content library.

C. This content library is optimized for syncing over HTTP.

D. There are active subscriptions on this content library.