For a live reading of "The Sun Has Long Been Set," the most appropriate effect to include would be a recording of nature sounds such as crickets chirping in the background. This choice aligns well with the themes of the poem, which often reflects on nature and the transition from day to night. The natural sounds would enhance the atmosphere and provide a fitting auditory backdrop for the reading.
The other options, while interesting, may not relate as directly to the overall mood and content of the poem.