A merchant asks you to extend customer functionality to allow customer accounts to be associated with two or more billing addresses.
A. By adding the attribute like customer_address_billing2 and customizing both My Account and Checkout functionality to use that new attribute
B. By changing the System Configuration setting: Customer>Allow multiple billing addresses to Yes
C. By altering the customer_entity table, adding the field billing_address2, and customizing both My Account and Checkout functionality to use that new field
D. This is out-of-the box functionality