Context: Jeffrey is painting watercolor pictures with his friend. An hour after they have finished, Jeffrey notices one painting is dry but the other is not. He wonders what factors affect how quickly watercolor paintings dry. So, he decides to design an experiment. He has the following supplies available:
two freshly painted watercolor pictures of the same size
his dining room table
a picnic table in his backyard
a heater
Using only these supplies, which question can Jeffrey investigate with an experiment?
A. Do watercolor paintings dry faster when placed next to a fan?
B. Does a large watercolor painting or a small watercolor painting dry faster?
C. Do watercolor paintings dry faster when they are placed inside or outside?
Pick the correct answer from the listed options and provide the letter of the selected option.

C