What is the primary purpose of using the technique of variable isolation in a scientific experiment?

To make the experiment faster to complete

To confidently establish a cause-and-effect relationship

To test as many different factors as possible in a single trial

To increase the number of possible outcomes from the experiment

A student wants to determine if the amount of sunlight a plant receives affects its growth. To correctly isolate the variable, which of the following experimental setups is the most effective?

Use two different plant species, each under different light levels.

Use two identical plants, but vary both the water and light for each.

Use identical plants, soil, and water, but vary the daily light exposure.

Use identical plants under different light, but place them in different soil types.

The results cannot be measured accurately.

The cause of the observed outcome is unclear.

The experiment will take too long to finish.

The initial hypothesis is automatically proven wrong.

The initial temperature of the coffee.

The material the cup is made from.

The volume of coffee in each cup.

The room temperature where the test occurs.