"canals constructed by an intelligent civilization" . . . . "canals visible on Mars" . "canals on Mars" . "canal" . "canals built on the planet Mars" . . "Martian channels" . . . "canals" . "paths" . "canal-like features" . "Martian canals" . . "canali" . "Martian canal" . . . . . . . . . . "linear features" . . . . "proposed canals" . "\\\"canals\\\" on Mars" . "ancient canal works" . "Martian canals" . "Martian ''canali''" . "\\\"channels\\\" (''canali'' in Italian) on the planetary surface" . "Mars contained canals" . . "channels on Mars" . . "canals of Mars" . .