HOTSPOT
You are managing multiple SharePoint sites. All users can access the home page on the root
SharePoint site.
When users try to access a subsite, they receive an error message stating that the site has not been
shared with them.
You need to allow users to request access to the subsite.
Which site setting should you configure? (To answer, select the appropriate site setting in the
answer area.)
Answer: 
Correct.
https://support.office.com/en-us/article/Set-up-and-manage-access-requests-94b26e0b-2822-49d4-929a-8455698654b3
Site owners can set up the access request feature so that it sends them an email when someone requests access to a site.
-Go to Settings Office 365 Settings button > Site Settings.
-Under Users and Permissions, click Site Permissions.
-On the Permissions tab, click Access Request Settings.
-In the Access Request Settings dialog box, select the check box next to Allow
access requests, and then type the email address of the person you want to
make responsible for approving access requests.
-Click OK.