The Lightning Component framework is used to develop:
Option B: Lightning Pages
Reference:
"Use Lightning components to build modern, responsive user interfaces for Lightning Experience and the Salesforce mobile app."
- Lightning Components Developer Guide: Introduction
Why Other Options Are Incorrect:
Option A: Salesforce Classic UI pages do not support Lightning Components.
Option C: Salesforce integrations are typically handled via APIs, not through Lightning Components.
Option D: Customized JavaScript buttons are not supported in Lightning Experience; alternatives are quick actions or Lightning Components.

* Controllers, helpers, and renderers are three resources in an Aura Component that can contain JavaScript functions. They are used to implement the client-side logic and behavior of the component12.
* Controllers are the primary resource for handling user interactions and events. They define the actions that are executed on the client or sent to the server12.
* Helpers are the secondary resource for sharing common code and logic across controllers and other helpers. They can also access component attributes and call server-side actions12.
* Renderers are the optional resource for customizing the rendering lifecycle of the component. They can override the default rendering, rerendering, and unrendering methods of the component12.
* Design and style are two other resources in an Aura Component, but they do not contain JavaScript functions. They are used to define the design-time attributes and the CSS styles of the component12.
References:
* 1: Aura Components Basics
* 2: Cert Prep: Platform Developer I: User Interface