Read the details below.
- Images of the Martian surface show dry canyons and river beds, sometimes marked with patterns of fossilized ripples.
- The Mars Curiosity rover collected extensive surface samples of clay that must have formed in the presence of water.
- Scientists believe that the dips in an ice-covered area of Mars indicate that a liquid lake may exist below the surface.
Choose the best topic sentence to introduce a paragraph containing these details.
Research examining the surface of Mars has led scientists to believe the planet once contained, and may still contain, liquid water.
Soil samples from the surface of Mars provide strong evidence that liquid water once existed on the planet.
ref_doc_title.
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