Answer:
Option “a” and “c”.
Explanation:
Option “a” and “c” are the positive externalities because the positive externalities are the ones that benefit to others. The activity of one person benefits the other person. So in the option, “A” neighbor put the birdhouses that will attract the birds that means another person who is a bird watcher will be benefited. Secondly, the investment in education will increase the country's GDP and the many people will be benefited from the education.