The News Reports That a Train Derailment 5 Miles from a Clinic

The news reports that a train derailment 5 miles from a clinic spilled a large amount of liquid chlorine that has been vaporized by the atmosphere.Which finding indicates that the chlorine gas is an imminent threat to the clinic?

A) Sighting of a low-lying green cloud.
B) Smelling "almonds" or "burning feathers."
C) Onset of sudden nausea in multiple patients.
D) Onset of skin blisters in multiple patients.