Aisha wants to examine the effect of room temperature on task performance. She places one group of participants in a room that is set to a temperature of 54 degrees, a second group in a room that is set to a temperature of 72 degrees, and a third group in a room that is set to a temperature of 90 degrees. She then measures the amount of time it takes each group to complete the same task. This design would best represent a(n) _____ design.