Which is the best way to revise this sentence? a) the valley was entered later on horse by the spanish, so the british and american trappers could enter by horse and on foot. b) arriving later, the spanish entered the valley by horse, while the british and american trappers entered by horse and on foot. c) the spanish entered the valley later by arriving on horse, but the british and american trappers entered by horse and on foot. d) the later-arriving spanish entered the valley by horse, and then the british and american trappers entered by horse and on foot.