The stimulus doesn’t establish how the asteroid would have killed the herbivores, so this doesn’t help. The correct answer must provide an effect of the asteroid sufficient to have killed all of the dinosaurs.

If anything, this makes the discrepancy harder to resolve since most dinosaurs being away from the strike’s vicinity could close off potential alternative explanations. This doesn't provide any alternative explanation as to how the asteroid killed the dinosaurs.

The scientists acknowledge that the cooling wouldn’t have lasted long enough to freeze the dinosaurs, so knowing the precise measurements of the cooling doesn’t help. We still don't have an alternative explanation for how the asteroid killed the dinosaurs.

This could explain how some of the dinosaurs were killed, but the scientists are talking about the global extinction of all dinosaurs. The correct answer must provide a way in which the asteroid could have killed all of them.

This provides an alternative explanation for how the asteroid killed all of the dinosaurs. Though the dust would have settled too soon to kill the plants or freeze the dinosaurs, these respiratory problems could have been what caused the extinction.