Suddenly, away on our left, I saw a faint flickering blue flame. The driver saw it at the same moment; he at once checked the horses, and, jumping to the ground, disappeared into the darkness." According to the context of this sentence, when the driver checked the horses, he A) made sure that the horses were okay. B) stopped the horses from moving forward. C) fed and made sure the horses were watered. D) took the horses into the veterinarian's office.