A person wearing a hat and carrying a knapsack walks uphill on a sand dune under a dark , cloudy sky and leaves the only visible footprints behind .
It is highly likely that a person in a hat who is carrying a knapsack leaves his footprints behind as he walks up a sand dune under a dark , cloudy sky .
It is highly likely that a person in a hat who is carrying a knapsack leaves his footprints behind as he walks up a sand dune under a dark , cloudy sky .
It is probably not the case that a person in a hat who is carrying a knapsack leaves his footprints behind as he walks up a sand dune under a dark , cloudy sky .
A person in a hat who is carrying a knapsack leaves his footprints behind as he walks up a sand dune under a dark , cloudy sky .