Fainting is a common symptom of heat stroke. The reason this happens to many people is the lack of fatigue. The best remedy is to keep yourself hydrated and have proper rest.
I hope it helps, Regards.
You can prevent the spreading of communicable disease by following through with Option C) avoiding sharing personal items, like toothbrushes. All of the other options can lead you to getting a disease, if you ignore hygiene you will never be clean, and if you avoid insect repellent you might get a disease from a bug, and if you cough/sneeze without covering your nose/mouth then you may catch a cold. Therefore pointing to the correct answer option C.
I hope this helps! Have a good day!