You need to enable the coauthoring of documents in the library

Your company uses Microsoft SharePoint Online for collaboration.
A document library is configured as shown in the following table.

You need to enable the coauthoring of documents in the library.
What should you do?

A.
Change the Who should see draft items in this document library? setting to Any user who can read items.

B.
Change the Create a version each time you edit a file in this document library? setting to No Versioning.

C.
Change the Require documents to be checked out before they can be edited? setting to No.

D.
Change the Require content approval for submitted items? setting to No.

Explanation:

From Technet Article “Overview of co-authoring in SharePoint 2013”
Check out – When a user checks out a document for editing, the document is locked for editing by that user. This prevents co-authoring. Do not enable the Require
Check Out feature in document libraries in which co-authoring will be used. By default, Require Check Out is not enabled in SharePoint 2013. Users should not
check out documents manually when co-authoring is being used.
https://technet.microsoft.com/en-us/library/ff718249.aspx