Explanation/Reference:
Explanation:
A: Cloud Witness is a type of Failover Cluster quorum witness that uses Microsoft Azure to provide a vote on cluster quorum.
Cloud Witness is a new type of Failover Cluster quorum witness that leverages Microsoft Azure as the arbitration point (figure below).
Figure: Multi-site stretched clusters with Cloud Witness as a quorum witness

As shown in the figure , there is no third separate site that is required. Cloud Witness, like any other quorum witness, gets a vote and can participate in quorum calculations.
E: The figure below illustrates a multi-site stretched Failover Cluster quorum configuration with Windows Server 2016.
Figure: Using a File Share Witness as a quorum witness

In case of power outage in one datacenter, to give equal opportunity for the cluster in other datacenter to keep it running, it is recommended to host the quorum witness in a location other than the two datacenters.
This typically means requiring a third separate datacenter (site) to host a File Server that is backing the File Share which is used as the quorum witness (File Share Witness).
References:
https://docs.microsoft.com/en-us/windows-server/failover-clustering/deploy-cloud-witness