The statement that is true about rebooting a virtual machine (VM) DB system node using the Oracle Cloud Infrastructure Console is D. On the VM DB system details page, find the node that you want to reboot, click the Actions (three dots) menu for that node, and then click Reboot. This is the procedure that is described in the official documentation12. It allows you to reboot a single node of a multi-node DB system individually, which may be necessary in some cases, such as scheduled maintenance1. The node is shut down and then restarted, and the floating IP address may take some time to be updated1.
A is incorrect, because the VM DB system nodes can be rebooted individually, as explained above. B is incorrect, because the VM DB system can be rebooted from the Oracle Cloud Infrastructure Console, as well as from the REST APIs or dbcli1. C is incorrect, because this is not the correct way to reboot a VM DB system node. Stopping and starting the DB system affects all the nodes, not just one, and it also stops and starts the database instances. This is different from rebooting a node, which does not affect the database instances1.
References: 1: Reboot a DB System 2: Reboot a DB System : Stop and Start a DB System