The correct answer is any substance or environmental factor other than a steroid
The independent variable is the factor or behavior that is manipulated by the experimenter in order to observe the effect of that manipulation on another factor or behavior that is the dependent variable. To you It is also called the experimental or active variable.
I don't know if this is correct but...... cherokee removal refers to the forced relocation in 1836 and 1839 ..... so I don't know if they was the answer u were looking for but that's all i know