What Makes Astronomers Believe That Mars Once Had Rivers and Running

Multiple Choice

What makes astronomers believe that Mars once had rivers and running water?

A) there is a grand canyon system about 2,500 mi long on its surface (all of it made by running water)
B) the volcanoes today show evidence of water coming from their highest points and running down (implying this would have happened even more long ago)
C) Images from orbiting spacecraft reveal ancient channels that look like dried-up river beds on Earth (and our rovers show geological formations made by running water)
D) giant basins (like Hellas) show evidence of being filled with frozen water that was once probably a sea
E) you can't fool me, there is no evidence at all that Mars ever had any water