What conditions must be met for private bargaining (the Coase Theorem) to be effective in resolving an externality

Which of the following is an example of a positive externality? a. promoting generic drugs would benefit people. b. a lower inflation rate would benefit most consumers. c. compulsory flu shots for all students prevents the spread of illness in the general public. d. singapore has adopted a comprehensive savings plan for all workers known as the central provident fund.