Salesforce Admin trained the employees on how to use Salesforce lightning. One of the users with a custom profile complained that he cannot switch to lightning, and the feature doesn’t exist for him. What would the Salesforce admin do to provide him access?

Answer options:

A.Change the user profile to Lightning
B.Add him as a new user in Salesforce and deactivate his old account
C.Add the user to the lightning access permission set
D.Create a workflow and add the user to it

Correct Answer: C 
Users require the Lightning Experience User permission to access Lightning Experience. By default, this permission is automatically enabled for all users with a standard Salesforce profile. Custom profiles don’t include the permission automatically. 
Option A is incorrect because having a profile related to lightning only doesn’t exist in Salesforce 
Option B is incorrect because adding the user as a new user cannot grant any extra permissions and it doesn’t have anything related to lightning 
Option D is incorrect because the workflow is a way to automate certain business processes and it is not related to lightning permission. 
Reference:

https://help.salesforce.com/articleView?id=lex_enable_users.htm&type=5