You create a Power Apps portal app and want to modify the layout of one of the pages. 
What portal element should you use?

Answer options:

A.Websites
B.Page Templates
C.Web Templates
D.Web Pages

Correct Answer: C 
If you want to modify the layout of the page, you need to use Web Templates. You can access the Web Templates list by opening the Portal Management (Number 1). The Web Templates contain the Liquid HTML code you can modify (Number 2). 
When you create a new Web template, you need to link it with a Page Template (Number 4). The Page Template helps to render the web page content in a browser. You can then use a new template in the Portal Studio to create the new page on your website. 

Option A is incorrect because the Websites item contains information about portal apps components, like web pages, web roles, web files.
Option B is incorrect because the Page Templates item provides information about the portal`s .aspx pages that display the web page content.
Option D is incorrect because the Web Pages item provides information on the portal`s web pages with their partial Url, parent page, and website.
For more information about the Power Apps portal, please visit the below URLs: 

https://docs.microsoft.com/en-us/powerapps/maker/portals/overview
https://docs.microsoft.com/en-us/powerapps/maker/portals/compose-page
https://docs.microsoft.com/en-us/powerapps/maker/portals/create-manage-webpages
https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/page-templates