A student observes a difference in the activity level of fish at a pet store. The fish in an aquarium near the window are swimming around more quickly tha the fish in an aquarium placed in the back of the store. The student forms a hypothesis about the effect of sunlight on fish activity levels and arranges to conduct an experiment. Which variable could be an independent variable in the student's experiment? types of fish sold speed of swimming fish amount of time fish were active temperature of water in fish tank