7. A study showing that people who consumed two or more servings of spinach per day had significantly better eyesight than people who ate less than one serving of spinach per week. Which of the following statements must be true? 1. This is an experiment, not an observational study. Il. This study provides evidence that eating spinach leads to better eyesight. Ill. The general diet and lifestyle of people who eat spinach could be a confounding variable. O I only O II only O I and II only O Ill only O ll and Ill only