it aint B, CDTs can be created from XSD/Scratch/Existing table or view/Another CDT

Option D is correct. The below explanation is in Appian documentation. Create New Version from XSD There are some configurations for CDTs that cannot be accessed through the data type designer. If you need to modify those configurations, you can download the XSD for the data type and re-import it to create a new version of the data type. To download the XSD file for a data type, click Download XSD in the settings menu of the data type designer. The following types cannot be downloaded as XSD: Simple types Fault types created by the Call Web Service Smart Service Once you have made the necessary changes to the file, click Create New Version from XSD in the settings menu and upload the new version of the XSD

In general, the option to "Create New Version from XSD" is most commonly used when creating a CDT that is used to consume or provide data through a Web Service. This is because the XSD file provides a standard way of describing the data structure used by the Web Service, which can be used to generate the CDT and ensure that it is consistent with the Web Service interface.