Which of the AWS service helps you to set reservation utilization and trigger alerts when utilization drops below the defined threshold?

Answer options:

A.AWS Budgets
B.Savings Plans
C.Reserved Instance (RI) Reporting
D.Reservation and Utilization dashboard

Answer: A
Option A is CORRECT. In AWS Budgets, you can set RI utilization budgets that define a utilization threshold and receive alerts when your RI usage falls below that threshold. 
Option B is incorrect. Savings Plans is a pricing model providing significant savings (up to 72%) upon committing to a consistent usage (measured in $/hour) for a 1- or 3-year term. AWS offers two types of Savings Plans, Compute Savings Plans and EC2 Instance Savings Plans.
Option C is incorrect. Reserved Instance (RI) Reporting is a cost management tool that helps customers to manage and monitor their instance reservations.
Option D is incorrect. Reservation and Utilization dashboard is incorrect.
References:
https://aws.amazon.com/aws-cost-management/aws-budgets/
https://aws.amazon.com/savingsplans/
https://aws.amazon.com/aws-cost-management/reserved-instance-reporting/