You create a new Dataverse plug-in. The plug-in monitors a company name change in the Accounts table. If the change happens, the plug-in emails the sales manager. The email text includes the alert about the change and provides the old and new company names. 
Please select the event stage for the registration of the new step for the Accounts update and additional registration attached to this step?

Answer options:

A.PreValidation
B.Post image
C.PreOperation
D.PostOperation
E.Pre image

Correct Answers: B, D and E 
The Dataverse plug-in is a .Net assembly that can modify the platform behavior. You can create your .Net project using a development environment, like Visual Studio or Visual Studio Code. After compiling the project and creating an assembly, you need to register the assembly and map the classes to the Event Framework events as logic business steps. 
There are three stages in plug-in event pipeline execution: PreValidation — an initial stage before the main operation. You can include the logic for canceling the event before the data transaction.
PreOperation — the next stage before the main operation but within the data transaction. You can make changes to the data in operation.
PostOperation — the stage after the main operation and still within the data transaction. You can call other actions using the Organization service before the message returns to the caller.
You create a plug-in that compares the company name before and after the table update. To accomplish this task, you need to use the table snapshots before and after the transaction. The Dataverse Plug-in Registration Tool provides an option to create a snapshot before (Pre image) and after (Post image). Following a plug-in registration, you register a new step (Number 1) for the Account table update (Number 2) and select PostOperation event stage (Number 3). 

Within this stage, you can call your plug-in and evaluate the images. But before that, you need to register the images for this step. On the Register New Image screen (Number 1), you select the step (Number 2) and check both Pre Image and Post Image boxes (Number 3). You provide the image name, the table alias, and select the table column as a parameter (Number 4) if needed. After you push the Register Image button, the tool would attach the image to the step. 

When you change the company name, the plug-in compares the account names before using the Pre image and after the update using the Post image and sends an email if there are any differences. 
All other options are incorrect. 
For more information about Pre and Post image use, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/developer/data-platform/register-plug-in#define-entity-images
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/register-plug-in
https://docs.microsoft.com/en-us/powerapps/developer/data-platform/tutorial-update-plug-in