In an appropriately designed experiment a scientist is able to test the effect of

The correct answer is an “Independent variable.” Nevertheless, this notion can be interpreted in several manners. Considering that the experiment model is formulated correctly according to the scientific method, the scientist will elaborate a hypothesis which contains a dependent variable, where:

A+B=C

Where A= dependent variable, B= independent variable, and C=predicted (work hypothesis) unpredicted (null hypothesis) result is possible. A dependent variable is where the effect will occur (for example diabetes mellitus) and a Xn independent(s) variable(s) is the one(or those ones) that will modulate it, either in a positive or negative way (a substance-a medication-, an intervention -exercise program- or behavior-change of eating habits-to mention some possible examples) the effect of the independent variable can be controlled in an experimental environment or not, occurring in a spontaneous or random form. Strictly, an experiment happens when both the dependent and the independent variable(s) are entirely controlled. Otherwise, the research is considered a quasi-experimental essay.  

disorders of the brain include both behavior disorders and other psychiatric illnesses. the primary difference between a behavior disorder and another type of psychiatric disorder is the presence of choice. psychiatric conditions are considered to be involuntary while in behavior disorders, choices are essential.

  b.

there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.