The most efficient way to write a Python script that interacts with web applications is to import the requests library. The requests library is a Python HTTP library that simplifies making HTTP requests to web servers, which is essential for interacting with web applications. It allows you to easily send HTTP/1.1 requests, without the need for manually adding query strings to your URLs, or form-encode your POST data. Options A and B involve creating a class or function for requests, which could be more time-consuming and less efficient than using a well-established library like requests. Option D, using the cURL OS command, is less efficient in a Python script since it involves calling an external command rather than using a native Python library.