Universal Container’s Salesforce Admin wants to share one of the opportunity records to one of the users without the need of creating sharing rule to do so. Which of the following would work to provide the user access to the opportunity record?

Answer options:

A.Permission set
B.Sharing rules
C.Manual sharing
D.Field level security

Correct Answer: C 
Sharing a record with only one user can be used through manual sharing. You don’t need to create any sharing rule for it. Manual sharing can be done through the manual sharing button which is called Sharing on the record page. Salesforce Admin needs to add this button on the page layout so that users can be able to use it. The button will only show if the organization button default is restricted to anything that is more than public read write. 
Option A is incorrect because the permission set cannot provide access to a record with only one user. 
Option B is incorrect because sharing rules is not required since it is only one record. 
Option D is incorrect because field level security is used to restrict access to a field. 
Reference: 

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