What combination of meteorological conditions is required for the formation of radiation fog?

1. High relative humidity, clear skies, and light winds of 2 to 5 knots.
2. Low relative humidity, overcast skies, and strong winds above 15 knots.
3. Warm moist air blowing over a cold ocean current, under calm winds.
4. Rapidly falling barometric pressure, warm rain, and convective instability.