Which of the following statements about search engine optimization techniques is/ are correct?

Which statement regarding website content is correct?

What authorizes payments for e-businesses and online retailers?

Which activities could be looked upon by Google as per their quality guidelines?

Which statement about Google's technical and quality guidelines is true?

What is the function of 'indexer' part of the Google search engine?

Sometimes robots.txt could still reference the URLs that you block, what is a better alternative against robots.txt?

Which Google crawler should you allow access to your web site’s mobile version?

Which is the reasons why your web site doesn’t show up in the results of a Google mobile search even using the site:operator?

What does it mean if nothing appears on doing search on the domain?

Which is the best keyword research technique?