Manipulative experiments alter levels of a predictor variable (or factor), and then measures how one or more variables respond to these alterations. ... Natural experiments-An observational study in which we take advantage of natural variation that is present in the variable of interest.
According to source. remain outside the danger (hot) zone is right.
Oxygen and Carbon Dioxide are the two gases being exchanged in the alveoli. Carbon Dioxide diffuses blood into the air, and oxygen diffuses from the air in the alveoli into the blood.
