Which of the Following Best Completes the Sentence,'______ Focuses on Earning

Which of the following best completes the sentence,'______ focuses on earning higher organic search engine rankings whereas ______ focuses on earning organic links to content.'?

A) Search engine optimization,social media optimization.
B) Social media optimization,search engine optimization.
C) Firm generated content,social media optimization.
D) Search engine optimization,user generated content.
E) None of these.