Research Summary: A circadian-rhythm study measured leaf movement in constant darkness and after timed light pulses. Hypothesis H: The rhythm is endogenous if it persists in constant darkness and can be shifted by a brief light pulse. Evidence summary: leaves continued a 24.3-hour movement cycle for five days in darkness; a 15-minute light pulse at subjective night shifted the next peak by 4.1 hours. Which evaluation is most accurate?