Explanation:

To determine the most efficient way for a developer to incorporate multiple JavaScript libraries in an Aura component, we must consider performance, organization, and Salesforce best practices regarding asset loading in the Lightning framework.

✅ Correct Answer: D. Join multiple assets from a static resource.
The most efficient and recommended approach in Aura components is to combine (join) multiple JavaScript libraries into a single static resource, then include that resource in the component. This method reduces the number of HTTP requests, improves performance, and ensures the libraries are available in the secure, controlled Salesforce environment.

Developers can use tools like Webpack or Gulp to bundle libraries (e.g., jQuery, Chart.js, Moment.js) into one minified file and upload it as a .zip file or single JS file to Static Resources. Then, in the Aura component, it is loaded using :

ltng:require scripts="{!$Resource.myBundledLibs}" afterScriptsLoaded="{!c.onLibsLoaded}"

This ensures that all necessary libraries are loaded efficiently and securely before the component executes its logic.
🔗 Reference: Salesforce Docs – Introducing Aura Components

❌ A. Use JavaScript remoting and script tags.
This option is misleading. JavaScript remoting is a way to call Apex methods asynchronously from JavaScript, not for loading libraries. Also, using raw <script> tags to load external libraries in Aura components violates Locker Service security policies and is strongly discouraged.

❌ B. Use CDNs with script attributes.
Loading libraries directly from CDNs (Content Delivery Networks) via script attributes is possible in raw HTML, but not secure or reliable in Lightning components, especially due to Locker Service and Content Security Policy (CSP) restrictions. Salesforce blocks or limits external script loading from untrusted domains for security reasons.

❌ C. Implement the libraries in separate helper files.
Helper files in Aura components are meant for custom application logic, not for including external libraries. You cannot just "implement" third-party JS libraries as helper files. This approach is incorrect and inefficient, especially for large libraries.

✅ Final Verdict:
D. Join multiple assets from a static resource is the correct and efficient solution for bundling multiple JS libraries in an Aura component, ensuring proper load order, performance, and compatibility with Salesforce security frameworks.