It is important to set goals because you will desire something higher than what you have now. It's important to share them with others so they can hold you accountable and make sure you are trying to achieve your goals.
A cool down routine is important after exercise because it helps to bring your heart rate down to a normal level after increasing it during exercise.
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!