Working With the HTTP Module in Node.js for RESTful Web Services

The correct answer to the question above is "The http module." Creating a RESTful web service in Node.js is made possible with the HTTP module.

The http module is an integral part of Node.js, allowing it to transfer data over the Hyper Text Transfer Protocol (HTTP). HTTP forms the backbone of any data exchange on the Web and it is a protocol followed for data communication. Using the http module, Node.js can act as a server, the basics needed to create a RESTful web service.

To use this in Node.js, you must use the require() function. The essential syntax for this is:

var http = require('http');

This simple line of code allows you to create a new http instance, which you can then use to listen to ports, read and write data, etc. From here, you can build your web service to accept and respond to various HTTP requests.

As an example, a basic server with Node.js and HTTP module could look like:

var http = require('http');

http.createServer(function (request, response) {
  response.writeHead(200, {'Content-Type': 'text/plain'});
  response.end('Hello World\n');
}).listen(8081);

console.log('Server running at http://127.0.0.1:8081/');

In the above code, http.createServer() includes a callback function which is run whenever an HTTP request hits the server.

Beside http, there are other modules like fs(file-system) which helps with file I/O operations, or the URL module which is used for URL resolution and parsing. These might also be of use, but for creating RESTful web services, the primary module is 'http'.

Finally, while the HTTP module is perfect for creating simple servers and RESTful APIs, for larger-scale applications, you might want to consider frameworks built on top of Node.js, like Express.js, which includes a range of pre-built features to improve efficiency and manageability.