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 table presents the average day and night temperatures in five cities. it also reveals whether a city receives substantial rainfall (wet climate) or little rainfall (dry climate). which city’s rocks are likeliest to experience frost wedging, and why? a) city a because the consistently subzero temperature would prevent water from melting b) city b because it is a wet region and the temperature fluctuates around the freezing point c) city c because it receives plenty of rain fall and the weather is moderately cool d) city d because the hot and dry weather would cause rocks to absorb water