"in an experimental study of the extent to which mental alertness is inhibited by sleep deprivation, mental alertness would be the"

In an experimental study of the extent to which mental alertness is inhibited by sleep deprivation, mental alertness would be the "dependent variable".

Dependent variable refers to a factor or phenomenon that is changed by the impact of a related factor or phenomenon called the independent variable.  

For instance, consumption is a dependent variable since it is caused and affected by another variable: wage. In a mathematical condition or model, the reliant variable is the variable whose esteem is to be dictated by that condition or model. In an experiment, it is the variable whose conduct under controlled conditions (that are permitted to change in a sorted out way) is considered.

answer; ///i believe the correct answer is (b) the writing of the ancients who lived in india after the indus valley inhabitants died out;

i got 3,4 and 5 as an answer