Explanation:
(a) Experimental unit
A person or an object, or some well-defined body or item on which some treatment is applied
(b) Treatment
Combination of a values of factors. These are explanatory variables.
(c) Response variable
The qualitative variable or quantitative variable in which the researcher wants to determine how the value is affected by any explanatory variable.
(d) Factor
It is the variable whose influence on a response variable can be assessed by the researcher.
(e) Placebo
An innocuous treatment, like a sugar tablet, which looks, smells and tastes like an experimental medication.
(f) Confounding
The effect of the two factors cannot be distinguished.
This is not true! There are many other such factors.
One of them is similar to food: the availability of water.
Other is also natural disasters: tsunamis, earthquakes... they also limit population from time to time. Similarly diseases such as Aids.
Answer:
Technically air. The air is the only thing known that we can, "hold" without ever having to use our hands for any known reasons. We're holding air right now. When you inhale or hold your breath, your lungs are holding air.
