Use the information below to answer the question following this description: Maggie read that some plants grow better if the soil is acidic.

#1: She wonders of a plant can really grow when it is exposed to acid.

#2: Maggie thinks that plants she will not grow better when acid is added to the soil.

#3: She puts potting soil in two planting containers and transplants two of her geraniums that seem about the same size into the pots. She puts the pots in the same location so that both get the same sunlight each are at the same temperature and she makes sure they get the same amount of water.

#4: However, Maggie puts a tablespoon of acidic vinegar in the water she gives to one of the plants.

#5: She measures the growth every week for five weeks.

#6: Maggie finds that the plants in the acidic soil had a greater height than those without acid.

QUESTION: Which statement number is describing the independent variable?

a. 3
b. 4
c. 5