the answer is: it was very thick/ lava was very thick
For Penn foster, I first answered (d) it flowed very quickly, but i got it wrong. I later found this in the lesson:
“Lava plateaus that form from flowing lava can be very thick. A particular feature known as basalt columnsmay form from very thick lava flows. As these thick flows pass over a flat surface, they tend to form jagged, hexagonal columns as they cool.”
hope I helped:)