What would be the standard way to let a user input quantity within the product configuration?

What would be the standard way to let a user input quantity within the product configuration?
A . By adding multiple rows to a container that references child products.
B . Create a regular attribute and push its value to the quote item quantity by a script.
C . This cannot be done in configuration, quantities belong to quote.
D . Add the itemQuantity attribute to the product and use it as Free input field in the configuration.

Answer: D