You need to add a client JavaScript code to the Main form of the Account table. 
Please select all the form element events that you can register the event handlers for.

Answer options:

A.OnReadyStateComplete
B.OnLoad
C.OnChange
D.TabStateChange
E.OnSave

Correct Answers: B and E 
Power Apps provides a Client API model for model-driven apps for users to implement for their business logic. The Client API model comprises objects and methods that developers can access using JavaScript code. They can create event handlers. The event handler includes the reference to the registered JavaScript web resource and the registration of the functions from the JavaScript code that the handler runs on the event occurrence. 
There are four form elements that you can register the event handlers for: Form — has two events: OnLoad (when the form loads) and OnSave (when the form’s data is saved).
Tab — has one event: TabStageChange (when the tab expands or collapses).
Column — has one event: OnChange (when column data is changed, or control loses focus).
IFrame — has one event: OnReadyStateComplete (when iFrame content loads).
To register an event handler for the JavaScript code on the main form, you need to add the code as a web resource to the library. You open the Dataverse table`s main form (Number 1), and on the Form libraries panel, push the "Add library" button (Number 3). After you register JavaScript as a web resource, it will be added to the library and appear on the Form libraries panel (Number 4). Then you switch to the Events tab (number 5). There are two events for the form: OnSave (Number 6) and OnLoad. When you open the OnSave or OnLoad sections, you can register an event handler using the "+ Event Handler" button (Number 7). This button opens the "Configure Event" pop-up (Number 8), where you can register the JavaScript function (Number 9) for this event handler. 

Option A is incorrect because the OnReadyStateComplete is the IFrame’s event, but it is not a Form’s event.
Option C is incorrect because the OnChange is the Column’s event, but it is not a Form’s event.
Option D is incorrect because the TabStateChange is the Tab’s event, but it is not a Form’s event.
For more information about the Dataverse event handler registration, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/configure-event-handlers-legacy
https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/use-main-form-and-components#configure-event-handlers