1) Exercise it by singing and hitting different notes, however don't go overboard
2) Make sure you don't overuse your voice, as well as trying to rest your voice when you are sick
3) Overall, have healthy habits, like not smoking and drinking a sufficient amount of water.
Making sure your children are safe and secure
Maybe when an organism has both an endocrine and a nervous system it is able to not only make rapid changes to be more well-adjusted in its enviroment but is also able to make changes required for survival in long-term.
Because vaccines have healthy viruses that try to get your body to be immune to the diseases so when you are already sick your body won't respond to the vaccine because it's just more viruses
