Context: Andy is washing dishes after cooking his dinner. He notices that some of the dishes still feel oily after being washed. He wonders what factors affect how clean dishes are after they are washed. So, he decides to design an experiment. He has the following supplies available:
a sponge
liquid dish detergent
a bar of soap
hot water
cold water
a pile of dirty dishes
Using only these supplies, which question can Andy investigate with an experiment?
A. Are dishes cleaner when washed with liquid dish detergent or with bar soap?
B. Are dishes washed in a dishwasher cleaner than dishes washed by hand?
C. Are dishes cleaner when washed with a soapy sponge or with a soapy rag?
Answer with the option's letter from the given choices directly.

A