In AWS billing, what option can be used to ensure costs can be reduced if you have multiple accounts managed by AWS Organizations?

Answer options:

A.Combined billing.
B.Consolidated billing - Volume Discounts.
C.Costs are automatically reduced for multiple accounts by AWS.
D.It is not possible to reduce costs with multiple accounts.

Answer – B
You can use the Consolidated Billing feature to consolidate payment for multiple Amazon Web Services (AWS) accounts or multiple Amazon International Services Pvt. Ltd (AISPL) accounts within your organization by designating one of them to be the payer account. 
For billing purposes, the consolidated billing feature of AWS Organizations treats all the accounts in the organization as one account. This means that all accounts in the organization can receive the hourly cost-benefit of Reserved Instances that are purchased by any other account.
Option A is incorrect because combined billing is itself the functionality of Consolidated billing.
Options C and D are just the distractors.
Reference:
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/useconsolidatedbilling-discounts.html
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/ri-behavior.html