The amount of pollution produced by cars was measured for cars using gasoline containing different amounts of lead. One car was used to test the four types of fuel: 10% lead gasoline, 15% lead gasoline, 20% lead gasoline, unleaded gasoline. In between the use of each the car's gas tank was emptied. The exhaust of the car was collected and analyzed. What is the independent variable?

The independent variable is the type of fuel

Explanation:

The independent variable in an experiment is the variable that is  being changed  in a scientific experiment. It is the cause of any of the observed outcomes of the experiment. The Independent variables is the variable that the experimenter changes to analyse its effect on the dependent variable(outcome).

In this case, the type of fuel (independent variable) is being changed and its effect on the amount of pollution (dependent variable) is observed.

the correct answer is:

a population changes in response to a change in the environment.

the framers of the constitution insisted that federal judges be nominated instead of elected due to their desire to have judges above the shifting whims of the masses.

the hope, whether achieved or not, was that federal judges would only be beholden to the law and that by not having judges be elected, they would be protected if that law dictated an outcome that ran counter to popular opinion.