Your team wants to begin practicing continuous delivery using CloudFormation, to enable automated builds and deployments of the whole, versioned stacks or stack layers. You have a 3-tier, mission-critical system. Which of the following is NOT the best practice for using CloudFormation in a continuous delivery environment?

Answer options:

A.Use the AWS CloudFormation ValidateTemplate call before publishing changes to AWS.
B.Model your stack in one template, so you can leverage CloudFormation’s state management and dependency resolution to propagate all changes.
C.Save CloudFormation templates in a source control system such as GitHub so that the scripts can be version controlled.
D.Parametrize the template and use Mappings to ensure your template works in multiple Regions.

Answer – B
Some of the best practices for Cloudformation are
Created Nested stacks
As your infrastructure grows, common patterns can emerge in which you declare the same components in each of your templates. You can separate out these common components and create dedicated templates for them. That way, you can mix and match different templates but use nested stacks to create a single, unified stack. Nested stacks are stacks that create other stacks. To create nested stacks, use the AWS::CloudFormation::Stackresource in your template to reference other templates.
Reuse Templates
After you have your stacks and resources set up, you can reuse your templates to replicate your infrastructure in multiple environments. For example, you can create environments for development, testing, and production so that you can test changes before implementing them into production. To make templates reusable, use the parameters, mappings, and conditions sections so that you can customize your stacks when you create them. For example, you can specify a lower-cost instance type for your development environments compared to your production environment. But all other configurations and settings remain the same. 
For more information on Cloudformation best practices, please visit the below URL:
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/best-practices.html