kristina says she has a theory about why earth is getting warmer. Which statement does Christina say that most likely demonstrate this theory

the last statement is correct i.e.

when your heart is not pumping enough blood around your body because your heart is severely failing, you may need an artificial heart. an artificial heart is a mechanical device, about the size of an orange, that is connected to your heart or implanted in your chest to or replace a failing heart.

because health skills are tools and strategies and also practical skills are also something you need to learn (like tools and strategies) and put it in reality.