The correct answer is D.
A cold front is a band of instability that occurs when a mass of cold air approaches a hot air mass. The cold air, being more dense, generates a "wedge" and gets under warm and less dense air.
Cold fronts move quickly. They are strong and can cause atmospheric disturbances such as thunderstorms, squalls, tornadoes, strong winds and short snowstorms before the cold front passes, accompanied by dry conditions as the front advances. Depending on the time of year and its geographical location, cold fronts can come in a succession of 5 to 7 days.
In weather maps, cold fronts are marked with the symbol of a blue line of triangles that indicate the direction of their movement, like the one in option D.
