Which revision corrects Sam’s error in the use of dashes to set off a clause in sentence 4? a The longhorns had been skittish, but Johnny Chillers, who was named for the old Chillers trail, sang to them—whenever they started to spook—to calm them down. b The longhorns had been skittish, but Johnny Chillers—who was named for the old Chillers trail sang to them—whenever they started to spook to calm them down. c The longhorns had been skittish, but Johnny Chillers—who was named for the old Chillers trail—sang to them whenever they started to spook to calm them down. d The longhorns had been skittish—but Johnny Chillers—who was named for the old Chillers trail, sang to them whenever they started to spook to calm them down.