单选题   Para. 1 ①Facebook enables advertisers to promote content to nearly 900,000 people interested in 'vaccine controversies'. ②Other groups of people that advertisers can pay to reach on Facebook include those interested in 'Dr Tenpenny on Vaccines', which refers to anti-vaccine activist Sherri Tenpenny, and 'informed consent', which is language that anti-vaccine propagandists have adopted to fight vaccination laws.
    Para. 2 Facebook's self-serve advertising platform allows users to pay to promote posts to finely tuned subsets of its 2.3 billion users, based on thousands of characteristics, including age, location, gender, occupation and interests.
    Para. 3 Facebook is already facing pressure to stop promoting anti-vaccine propaganda to users amid global concern over vaccine hesitancy and a measles outbreak in the Pacific north-west.
    Para. 4 On Thursday, California congressman Adam Schiff, the chair of the House intelligence committee, cited the Guardian's reporting on anti-vaccine propaganda on Facebook in letters to Mark Zuckerberg and Google CEO Sundar Pichai urging them to take more responsibility for health-related misinformation on their platforms.
    Para. 5 'The algorithms which power these services are not designed to distinguish quality information from misinformation or misleading information, and the consequences of that are particularly troubling for public health issues,' Schiff wrote.
    Para. 6 'I am concerned by the report that Facebook accepts paid advertising that contains deliberate misinformation about vaccines,' he added.
    Para. 7 ①Facebook's ad-targeting tools are highly valued by businesses because they enable, for example, a pet supply store in Ohio to show its advertising exclusively to pet owners in Ohio. ②But the tools have also spurred controversy.
    Para. 8 ①Facebook said it was looking into the issue. ②'We've taken steps to reduce the distribution of health-related misinformation on Facebook, but we know we have more to do,' a Facebook spokesperson said in a statement responding to Schiff's letter. ③'We're currently working on additional changes that we'll be announcing soon.'
    Para. 9 ①The changes under consideration include removing anti-vaccine misinformation from recommendations and demoting it in search results, the spokesperson said. ②The steps they have already taken include having third-party fact-checkers review health-related articles.
    Para. 10 A Google spokesperson declined to comment on Schiff's letter, but noted the company's recent changes to its recommendation algorithm to reduce the spread of misinformation, including some anti-vaccine videos.
    Para. 11 ①'We've done a number of things within this realm,' the spokesperson said. ②'But these are still early days. And our systems will get better and more accurate.'
    Para. 12 ①Schiff introduced a House resolution declaring 'unequivocal congressional support for vaccines' a few years ago. ②He told the Guardian that he plans to introduce a similar resolution again this year, but that he may update it to feature 'the role that these social media companies are playing in the propagation of this bad information'.
    Para. 13 ①'It's difficult to understand why, when this problem has been raised, why either company would take advertising dollars to promote dangerous and misleading information,' Schiff said. ②'I think Our chances of passage are far better than they have been in the past, and tragically that's because we've seen the problem just grow and grow.'