Which Statement BEST Describes Our Current Understanding of the Valles

Which statement BEST describes our current understanding of the Valles Marineris?

A) The valley system appears to have been carved almost entirely by water flowing toward the lowlands from the geological rise near Olympus Mons.
B) The valley system appears to be a set of parallel subduction trenches along the boundary where the northern lowlands are colliding with the southern highlands.
C) The valley system appears to have formed entirely by cracking and faulting of the Martian surface, without noticeable intervention of erosion by water.
D) The valley system formed primarily by cracking and faulting of the Martian surface, but some valleys at the eastern end appear to have been carved by water.