https://www.reuters.com/article/us-facebook-zuckerberg/facebooks-zuckerberg-hits-pause-on-china-defends-political-ads-policy-idUSKBN1WW2LJ >Facebook Inc Chief Executive Mark Zuckerberg on Thursday defended the social media company's political advertising policies and said it was unable to overcome China's strict censorship, attempting to position his company as a defender of free speech.