Q: The mars rover collected round clumps of crystals that, on earth, usually form in what?


Read this paragraph and choose the correct option from the provided answers:

The ice ages were very recent as Earth history goes. The animals are familiar, but they're still very different from modern ones. For one thing, most of them were huge. A small surface area-to-volume ratio is better for keeping warm (less surface to lose heat from). Although the dominant animals were mammals, the Pleistocene Earth still does not look quite modern.

 Choices:

- rocks

- volcanoes

- air

- water


A:
water