You create a Component library and add a new component. Then you create a new canvas app and import the component from the library. After some time, you update the component and publish a new version. 
How will the Component library deliver the update?

Answer options:

A.The Component library updates the component instances automatically
B.The Component library sends an email with a link for a download of the new component version
C.The Component library posts a message inside the canvas app about the new component version
D.The Component library posts a message about library updates when you open the canvas app
E.The Component library posts a message in the Power Apps apps browser about the new updates

Correct Answer: D 
The Components are reusable blocks that help you develop the Power Apps applications. Power Apps provides out-of-the-box standard controls (components), like HTML Text, Vertical Gallery, or Edit Form. If your Power Platform solution requires more than standard controls, Power Apps also provides tools to create and reuse the custom code components. 
The best way to store, maintain, and share reusable components is to put them in the Component library. When you want to add a component to your canvas app, you can easily use the Component library for the component import. Also, the Component library helps users with the component’s updates. 
Suppose you update and publish the component in a Component Library. The next time you open any canvas application that uses the updated component, you will see the library update message (Number 1). The message does not specify the component or components that are updated. You can push the Review button (Number 2) to see the update details. 

The Review Update screen provides only the Component library name (Number 1), update date (Number 2), and the version note (Number 3). 

Because the Component library provides minimal information about the component update on the review screen, the update description can be crucial. The makers can put detailed information in the version note (Number 3) when they save the component update (Number 1) in the Component library (Number 2). 

All other options are incorrect. 
For more information about canvas apps Component libraries, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/component-library
https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/component-library?#update-a-component-library