You need to troubleshoot the issue

You are the Office 365 administrator for your company.
Users report that they cannot sign in to Lync from their mobile devices, but they are able to send and
receive Lync messages by using their laptop computers.
You need to troubleshoot the issue.
What should you do?

A.
From the Office 365 message center, confirm Lync settings.

B.
Use the Microsoft Connectivity Analyzer tool to confirm settings.

C.
Confirm Lync user licenses for the affected users.

D.
From the Lync admin center, verify the external access settings.