Which of the following scenerios fits all of the criteria for the two-source interference equations to be valid?

1 An observer is standing far away from two red LED signal lights.
2 Light from an incandescent bulb shines onto a screen with a single slit; then the light shines onto a screen with two slits in it and the light from the two slits finally shines onto a far-away screen.
3 An observer stands on a road far away from two neighboring radio towers for different radio stations.
4 Light from an incandescent bulb shines onto a screen with a single slit; then the light shines onto a screen with two slits in it and the light from the two slits finally shines onto a nearby screen.
5 An observer stands on a road that runs five kilometers away from the two synchronized transmitting towers for a radio station.