What would be the control in this scientific experiment?

I'm taking biology right now and I just did a lab on the digestive process of the stomach. I have 6 test tubes. Test tube 1 has 5 mL of distilled water and chopped piece of boiled egg albumen. Test tube 2 has 5 mL of hydrochloric acid and a chopped piece of boiled egg albumen. Test tube 3 has 5 mL of a pepsin solution and a chopped piece of boiled egg albumen. Test tube 4 has 5 mL of hydrochloric acid and powdered pepsin mixed in with a chopped piece of boiled egg albumen. Test tube five has the same solution as test tube 4 but the chopped egg albumen is chopped even further. Test tube 6 has the same solution as test tube four with the egg piece left intact. Only test tubes 1-5 are put in an incubator at 37 degrees Celsius. I first thought it was test tube 6 because it was set at room temperature but would it be test tube 1 because it contains distilled water?