Can someone explain why it is A and not D?

@ciarataheri, (D) is incorrect because it suggests that it is necessary to continuously play advertisements across the screen in order to offer the computers free of charge, whereas the argument only allows us to conclude that to offer computers free of charge, advertisers must see increased sales as a result of this precise targeting: free computers -> increased sales Sure, one of the options to increase sales described in the argument is to play ads continuously but could we conclude that it is the only way as (D) suggests? No, the argument never precludes the possibility that ads could be played only in certain hours for example, and still result in increased sales Since we cannot definitely conclude that ~ continuous ads -> ~ increased sales ->~ free computers, (D) is an unwarranted inference. (A) is correct because it properly concludes that in order for advertisers to offer computers free of charge, there must be at least some increase in associated sales. Let me know if you have any other questions.