The best and most correct answer among the choices provided by the question is the third choice "call 911"
Tachycardia = Too fast. A heart rate of more than 100 beats per minute<span>(BPM) in adults is called tachycardia. What's too fast for you may depend on your age and physical condition.</span>
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The principle of science used here is uncertainty. The various doctors attributed their sickness to hookworm gotten from cat and dogs but the uncertainty here is that it wasn't described they had access to the water because they were disappointed by the feces of dogs and cat found around, and how they all got the same rashes at the same time is questionable