Multi-select: Knowing that "a warm front causes cloudy and rainy weather", how would one answer "Tom noticed it was getting gloomy outside at only two in the afternoon. Which of these might be the cause?"

pick from the following.
(a). the witch at the top of the hill has placed a spell on the town.
(b). a warm front has moved overhead.
(c). a funeral is about to start at the church across the street.
(d). the earth is moving through a dark area of space....A:
(b).