Personally, i agree with both two and three, however, the one that makes the most sense to me would be 2 because of the fact that you can find sufficiently adequate information on both peer-reviewed journals and non peer reviewed
To answer it precisely correct, I would have to know the context which the first sentence refers to ('...and is you have any doubt...'). But everything that comes after it, serves simply to illustrate a really silly situation. It deliberately has nothing to do with the context, with the intention to emphasize a point of view/opinion, while giving the text a certain humorous content. It's a common writing technique.
The previous context probably has something to do with pointing out the silliness of some situation or behavior, right?
The basic needs for the survival of all living organisms are the same. All living organisms need to respire, digest food for obtaining energy, and get rid of metabolic wastes. Cells are capable of performing all the metabolic functions of the body. Hence, cells are called the functional units of life.
Hurt,in pain.ache/d.sicken
The correct answer among the choices provided is the second option. He was interested in being completely surrounded by nature. Walden shows that one can live simply with the natural surroundings. It is also a work about spiritual quest and a social experiment.