A scientist is testing a new fertilizer. They give one plant the new fertilizer and double the amount of water it receives. A second, identical plant receives no fertilizer and the normal amount of water. To make this a fair test of the fertilizer, what is the most important change the scientist should make?

Use two different types of plants.

Give both plants the same amount of water.

Place one plant in sunlight and the other in shade.

Add even more fertilizer to the first plant.

An engineer wants to test how a car's speed is affected by tire pressure, engine size, and vehicle weight. Testing all these on a real car is complex. How could a computer simulation be a useful tool for this engineer?

A simulation can change all the variables simultaneously for a faster result.

It can easily test each variable one at a time.

A simulation can prove the car is perfectly safe.

It can build a physical model of the car automatically.

To get the desired result as quickly as possible.

To prove a pre-existing hypothesis is always correct.

To ensure that only one variable is changed at a time, allowing for a clear cause-and-effect conclusion.

To use as many variables as possible to see what happens.

The experiment did not last long enough to be valid.

Corn seeds are always harder to grow than bean seeds.

They changed the soil type, plant type, and amount of light all at once.

The student should have measured the plants every single day.

It makes the experiment take twice as long to complete.

The results will simply be the average of the two changes.

It is impossible to determine which variable was responsible for the observed change.

The experiment becomes too expensive and complicated to perform.