What type of variables are factors that are being tested in an experiment and varied by the experimenter?

What trade did europeans want most before the 1800s ivory wood slaves gold

Which environmental change allowed people to travel by land between asia and north america a.human apaption to arctic environments b.the introduction to horses to north america c.the formation of ice sheets on land d.a rise in ocean temperatures

Which of the following actions do the national response and recovery policies (national response framework, national infrastructure protection plan, national incident management system) not provide guidance on?