If you found some sandstone in an ancient river bed, which of these conditions at the time that the sandstone was formed would be easiest to understand?

a. what the climate was like
b. how old the particles were
c. how fast the river was flowing
d. when the particles were deposited

I believe that the answer to this would be option C. Since sandstones are not commonly seen among river beds, the condition that would make us easier to understand as to what happened to this is how fast the river was flowing. Due to the pressure of the river, this brought other sediments with it most especially sandstones.