Insurance, if you have mileage limits, preparing for weather, choosing the car.
The correct answer would be the second option. The correct plan for his experiment would be that the temperature, the type of limestone, and the type of acid are controls. The amount of acid and the amount of damage to the limestone are variables. To determine the degree of damage of the acid it would be best that the amount of acid is the manipulated variable while everything else are assumed constant.
Christianity is the correct anwser
You are likely seeing a cognitive therapist.
Learning therapists are there to help you learn and study better; behavioral therapists are there to change the way you behave; psychodynamic therapists want to elicit your unconscious thoughts. So, if you have all of this in mind, the only therapist left is cognitive therapist, who is there to change your thoughts.