Which of the numbered features is a pyroclastic flow?

Question

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Pyroclastic flows are rapidly-moving, high-temperature mixtures of volcanic ash, rock fragments, and gas that flow down the sides of a volcano during an eruption. They generally move too fast and too close to the ground to be seen as a distinct cloud (like choice A), and they do not form as a result of lava squeezing through a stable vent (like choice B). The ash cloud visible in choice C is likely a result of an explosive eruption, but it does not depict the characteristic flow of a pyroclastic flow. Choice E is a video link and therefore not a valid answer. Therefore, the most likely depiction of a pyroclastic flow is choice D, which shows a rapidly-moving mixture of ash, gas, and rocks flowing down a hillside.

Which of the Numbered Features Is a Pyroclastic Flow