1. A full stack service with 3 years of experience would likely be a robust and well-designed web application that is built to handle a variety of different user needs. 
It would be built with a variety of front-end and back-end technologies (interface graphic,  scripting ... )
including languages such as :
- JavaScript - Nodejs, JQuery, React 
 - PHP  - Laravel
 - Java - Spring boot
 - Python - Flask , Django
 
The service would be able to handle a large number of concurrent users, and would be optimized for performance, scalability, and security.