"During installation, you can select the server to be in staging mode. This action makes the server active for import and synchronization, but it does not run any exports. A server in staging mode is not running password sync or password writeback, even if you selected these features during installation. When you disable staging mode, the server starts exporting, enables password sync, and enables password writeback." https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-staging-server

D. Run Azure AD Connect and disable staging mode.

D is correct "Suppose you have an Azure AD Connect with Password Hash Synchronization feature enabled. When you enable staging mode, the server stops synchronizing password changes from on-premises AD. When you disable staging mode, the server resumes synchronizing password changes from where it last left off. If the server is left in staging mode for an extended period of time, it can take a while for the server to synchronize all password changes that had occurred during the time period." https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-staging-server

Disable Staging mode, D is correct! https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-staging-server

The given answer D is the correct answer.

The question (and answers) is not precise, because if staging mode is enabled, then it suppresses the exports from running but still run import and synchronization.