Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: (CNN) Since the discovery of dark streaks on the slopes of Mars in 2011, astronomers have been excited about potential evidence of water beneath the surface of the red planet. If there are subsurface water flows on Mars, they could allow life -- even on a microbial level -- to exist as well. But further study of these recurring slope lineae, known as RSL, is revealing something else. Those dark streaks may be the result of granular flows like sand and dust, according to a study published Monday in the journal Nature Geoscience. The study is the product of a research team made up of representatives from the US Geological Survey, the Planetary Science Institute, the University of Arizona and Durham University in England.The flows correlate more with sand on active dunes rather than subsurface waterResearchers studied flows at 10 sites 
 Question:Earth is the only analog we have for Mars, but _ obviously behaves differently, the researchers said.

Mars