Pick up the one having the broadest valley:

Explanation

Option A is correct: The absorption spectrum of chlorophyll a features the broadest valley around 520-530 nm, indicating the least effective absorption in this green region. This contributes to the green appearance of plants because green light is not absorbed effectively and is reflected. Option B is incorrect: Carotenoids have absorption valleys, but these are narrower than those of chlorophyll a. They absorb light in different regions, such as the blue and violet, helping to capture a broader spectrum of light for photosynthesis. Option C is incorrect: Chlorophyll b's valley in the green region is not as broad as chlorophyll a's, making it less effective in absorbing green light. It primarily absorbs light in the blue and red regions. Option D is incorrect: Not all pigments have equally broad valleys; chlorophyll a is distinct in having the broadest valley among the options provided.