The Configuration Type field defines when users can access the Configure Products page and whether they are required to configure certain options. Your configuration type also determines the configuration events you can choose from.
Allowed: Salesforce CPQ directs users to enter the configurator when they perform any of the selected configuration events. In the configurator, they can change their bundle or leave without making any changes.
Required: Salesforce CPQ directs users to enter the configurator when they perform any of the selected configuration events. In the configurator, they can change their bundle or leave without making any changes. This value performs a different function if you’re configuring a nested bundle with a required configuration type. In this scenario, Salesforce CPQ displays a red vertical line next to the radio buttons or checkboxes of any required configurations that you have not yet entered. If you try to save in the configurator without configuring those options, you receive an error message.
Disabled: Prevent the user from ever altering the bundle in the configurator. Salesforce CPQ instead uses this bundle’s default product option setup when you add it to a quote....

Correct Answer should be - 'D'