Acid rain is a especially a problem in cities because of the toxic waist.
THE ANSWER IS b ALL VOTERS HOPE THIS HELPED :)
Because their geography is close together and Mongolia was an empire wanting to expand
I believe the answer is: No, this does not need to be reported since it is unrelated to participation in the study.
Unless a person is induced with chemical substance, The cause of heart attack is most likely diet and lifestyle that has been building up over time.
Since the research is revolved around attitudes towards hygiene and disease prevention, they would only observe the subject's behaviour, not making them digesting any substance.