input: Write a function to download articles from a given list of URLs and save them to files.
  assert download_articles(['https://www.example.com/article1', 'https://www.example.com/article2']) == ['article1', 'article2']
  assert download_articles(['https://www.example.com/article3']) == ['article3']
  assert download_articles([]) == []
output: import os
  import requests
  
  def download_articles(urls):
      filenames = []
      
      for url in urls:
          response = requests.get(url)
          filename = url.split('/')[-1]
          with open(filename, 'w') as file:
              file.write(response.text)
          filenames.append(filename)
      
      return filenames