A developer created an Apex class that updates an Account based on input from a Lightning web component that is used to register an Account. The update to the Account should only be made if it has not already been registered.

What should the developer do to ensure that users do not overwrite each other's updates to the same Account if they make updates at the same time?

A software company uses a custom object Defect_c, to track defects in their software, Defect__c has organisation-wide defaults set to private Each Dafect__c has a related list of Reviewer_c records, each with a lookup field to User that is used to indicate that the User will review the Defect_c.
What should be used to give the User on the Reviewer_c record read only access to the Defect_c record on the Reviewer_c record?

Which method should be used to convert a Date to a String in the current user's locale?

A developer created and tested a Visualforce page in their developer sandbox, but now receives reports that users are encountering ViewState errors when using it in Production. What should the developer ensure to correct these errors?

Which use case can only be performed by using asynchronous Apex?