$10$ points

Frank wants to develop a technique for dyeing shirts so that the color of a design on the shirt does not fade after it is washed. Identify the following activity as an observation, a hypothesis, an experiment, or a conclusion.

Frank notices that the dye faded on the shirts that were soaked in water, salt water, or the mixture of baking soda and water. However, the dye on the shirt that was soaked in vinegar did not fade.

a$.$ observation

b$.$ conclusion

c$.$ hypothesis

d$.$ experiment