You open the settings for the site collection and discover that the External sharing option cannot be configured.
You need to ensure that the site collection can be shared to external users.
What should you do first?

A.
From the Microsoft SharePoint admin center, modify the External sharing setting.

B.
From the Microsoft SharePoint admin center, modify the bcs settings.

C.
From Office 356 PowerShell for SharePoint Online, set ShowEveryoneClaim to $true.

D.
From Office 365 PowerShell for SharePoint Online, set SharingDomainRestrictionsMode to AllowList.

Explanation:
Turn external sharing on or off for a SharePoint Online environment (tenant)
You must be a SharePoint Online administrator to configure external sharing.
1. From the SharePoint admin center, click sharing.
2. Select one of the following:
Select one of the following:

https://support.office.com/en-us/article/Manage-external-sharing-for-your-SharePoint-Onlineenvironment-c8a462eb-0723-4b0b-8d0a-70feafe4be85