Which of the following statements about Google's technical and quality guidelines are true?

Q) Which of the following statements about Google's technical and quality guidelines are true?

Answers:
• It is advantageous if your web server supports the If-Modified-Since HTTP header
• If using dynamic pages, it helps to keep the parameters short and the number of them few
• Avoid using robots.txt to prevent crawling of search results pages or other auto-generated pages, even if they don't add much value for users coming from search engines
• Submitting new pages of your website at http://www.google.com/addurl.html as soon as they are online, helps to speed up indexing