Omar observes that many buildings in his city were built using limestone. He has read that acid rain can damage limestone. He also knows that limestone reacts with acids and that chemical reactions are affected by temperature. With this in mind, he conducts an investigation to see how the amount of damage to the limestone is affected by the amount of acid on the stone.

Which statement describes the correct plan for his procedure?

The temperature and the amount of damage to the limestone are controls. The amount of acid and the type of limestone are variables.
The temperature and the type of limestone are controls. The amount of acid and the amount of damage to the limestone are variables.
The amount of acid and the type of limestone are controls. The temperature and the amount of damage to the limestone are variables.
The amount of acid and the amount of damage to the limestone are controls. The type of limestone and temperature are variables.