Concept:For a starch test, the leaf must contain starch made during photosynthesis.Explanation:Starch is formed in leaves only when sunlight is available for photosynthesis.Plucking the leaf after it has been exposed to sunlight ensures that starch has been produced and can be detected.At other times, such as before sunrise or after sunset, the leaf may have little or no starch.Answer:A. after being exposed to sunlight