You create a new ribbon button for a model-driven app. You want the app to enable the button on the main screen when the text field is changed. And if a user clicks the new button, it opens the web page. 
What command button elements should you use to achieve your goal?

Answer options:

A.Command function
B.Rule
C.Call
D.Action
E.Component

Correct Answers: B and D 
When you create a new command button, you need to address two elements: rule and actions.
The rule defines when button’s state within the application, like enable/disable state of the button when some field is changed or who can see the button. There are two types of rules: enable (should the command button be enabled) and display (should the rule be visible for the users). 
The action describes the button behavior, like what should happen when the button is clicked. There are two types of command button actions that users can define in the OnClick event: execute the custom logic using JavaScript code or open a specific URL. It can be the dynamic URL if the business logic of your app requires it. 
All other options are incorrect. 
For more information about the Command button rules and actions, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-enable-rules
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-display-rules
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-actions
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-commands