Darla learned about the growth of wildflowers in her area. She wanted to study the Blanketflower, which is a plant that is native to Florida. Darla tested how far apart seeds should be planted in order to get the healthiest flowers. She followed this procedure: In early spring, obtain a bag of Blanketflower seeds. Prepare two 10 m2 plots outdoors for planting. They should be close to each other. Plant seeds in one plot 20 cm apart, and plant seeds in the other plot 10 cm apart. Observe and record the growth once a week for one year. Two years later, she shared her procedure and results with a friend of hers who lived hundreds of miles north of her in Michigan. Her friend replicated the experiment in Michigan by following the exact same procedure that Darla did. When they compared data, they had different results. Which of the following best describes the replication of Darla's investigation? a The replication is likely invalid because of weather differences between the two investigation locations. b The replication is likely valid because in both investigations, the same type of flowers were tested outdoors c The replication is likely invalid because two different people conducted the investigation. d The replication is likely valid because in both investigations, the seed-planting distance was the variable.