Refer to figure.
Frontal fog forms in the cold air ahead of an advancing warm front. 

As warm frontal precipitation  falls from the warm moist air above the frontal surface through the cold air below, the raindrops evaporate partially into the cold air. This evaporation adds moisture to the cold air until it reaches saturation and fog forms. The process of warm rain falling into cold air and evaporating to saturate it is the defining mechanism of frontal fog. 

It forms in the cold sector ahead of the warm front surface at the ground and can produce very dense, persistent fog that creates severe IFR conditions. Frontal fog often extends over wide areas ahead of warm fronts and can be one of the most hazardous fog types for aviation due to its wide extent and persistence.

Frontal fog → CORRECT. Frontal fog forms ahead of a warm front when rain falling from the warm moist air mass above the frontal surface evaporates into the cold air below, saturating it and forming fog.

Radiation fog → INCORRECT. Radiation fog requires clear skies for longwave radiation cooling of the surface and calm or very light winds. These conditions are associated with anticyclonic situations, not approaching warm fronts which bring increasing cloud cover and wind. Radiation fog cannot form under the overcast cloud associated with an approaching warm front.

Advection fog → INCORRECT. Advection fog forms when warm moist air moves horizontally over a cooler surface and is cooled to its dew point. While advection fog is associated with maritime environments and temperature contrasts, it is not the specific type associated with warm frontal precipitation processes. The mechanism is different from frontal fog.

Upslope fog → INCORRECT. Upslope fog forms when air is forced up sloping terrain and cools adiabatically to its dew point. It is a local orographic phenomenon and is not associated with the broad-scale warm frontal system described in the question.