How can a developer implement this feature?

Given the following Anonymous Block:

Which one do you like?
What should a developer consider for an environment that has over 10,000 Case records?

Which code in a Visualforce page and/or controller might present a security vulnerability?

A custom object Trainer_c has a lookup field to another custom object Gym___c.
Which SOQL query will get the record for the Viridian City gym and it's trainers?

A developer must provide custom user interfaces when users edit a Contact in either Salesforce Classic or Lightning Experience.
What should the developer use to override the Contact's Edit button and provide this functionality?