A. In each order item, set Complete Delivery to required.
This setting (value 'C' in the partial delivery indicator) explicitly prevents partial deliveries for the item, which is the opposite of the requirement.
B. In the order header, set Order Combination to allowed.
This setting allows multiple, separate sales orders to be combined into a single delivery; it does not control partial delivery behavior within a single sales order.
C. In the order header, set the Complete Delivery indicator.
This indicator forces all items in the entire order to be shipped together in one delivery, completely disallowing any partial deliveries for the order.