Why do pumice stone float on the surface of the water? A: They are<br/>comparatively smaller. B: They contain special <br/>materials. C: They are not real stones. D: There are pores in the stone.

How did “columnar joints” come into being? A: The magma condensed into stone columns. B: The pumice stones piles layer by layer. C: The volcanoes look like columnar joints. D: Creatures were gradually fossilized and they slowly turned into a thick limestone layer on the seabed