Answer:
I am answering the second one btw, so here we go
A gradually but completely withdrawing from alcohol or drugs.
Nutrition is an important thing in regards to quality of life. With adequate nutrition your body will have the nutrients and vitamins that are vital in keeping the homeostasis of our bodies intact, and when this happens, you are feel good. However without adequate nutrition you are predisposed towards diseases that result directly from the lack of adequate nutrition (Like Bari-Bari if you lack Vitamin b12) or your body is inadequate when fighting illnesses like the flu because it doesn't have the energy and nutrition required to help fight.
I'm actually in online school at the moment and I've also been behind quite a bit, my best advice is try to get in contact with the teachers, I don't know if your online school has a center where you can go in and get help but mine does and if you just tell them what you are going through I'm sure that they can help. Worse case scenario you wanted to take a few days off from school and you'll have to lie about being sick or something and they will understand. I hope I helped.
Four conditions are needed for natural selection to occur: reproduction, heredity, variation in fitness or organisms, variation in individual characters among members of the population
