input: Write a python function to scrape article titles from a webpage using BeautifulSoup and filter them by a keyword.
  assert ScrapeTitles('data science') == ['Data Science 101', 'Advanced Data Science Techniques']
  assert ScrapeTitles('machine learning') == ['Machine Learning Basics', 'Deep Dive into Machine Learning']
  assert ScrapeTitles('python') == ['Python for Beginners', 'Python Data Analysis']
output: def ScrapeTitles(keyword):
      import requests
      from bs4 import BeautifulSoup
      
      url = 'http://example.com/articles'  # Placeholder URL
      response = requests.get(url)
      soup = BeautifulSoup(response.text, 'html.parser')
      
      titles = [title.get_text() for title in soup.find_all('h2', class_='article-title')]
      filtered_titles = [title for title in titles if keyword.lower() in title.lower()]
      
      return filtered_titles