CustomerAddresses - Displaying Different Selections For Billing / Shipping Dropdown

I need assistance understanding how address information is pulled into the Billing and Shipping dropdowns in Checkout.

I am new to MVC and have some web development experience.

I've spent a lot of time digging through all the solution files in Visual Studio in an attempt to understand how information is extracted and populated.  I know that the CustomerAddress table must be leveraged in order to select only the addresses associated to the current customer but I cannot find any reference to Customer_ID in the CustomerAddresses table in any files.  In SQL,  it would as simple as writing something like "Select * From Address Inner Join CustomerAddresess on Address.ID = CustomerAddresses.Address_ID Where Customer_ID = @CurrentCustomerID".

I would be very greatful if someone could explain to me how this occurs in nopCommerce.

Thanks in advance for any assistance.
DB.

Nevermind. Found what I was looking for.
Not sure why I had such a hard time finding the OpcBillingAddress.cshtml and OpcShippingAddress.cshtml files.