Answer:
Green color filter
Explanation:
It is given that Duckweed grown on water and covers all part of the pond very rapidly. In order to limit their growth is proposed to use a color panel so as to shield the ponds and inhibit photosynthesis process and also kill the pests.
So a green colored panels can be used to shield the pond. This is because the photosynthetic pigments such as the chlorophylls absorbs all the green frequencies of the visible light except for the wavelength that corresponds to the green color. Therefore, by using a green filter, the wavelength corresponding to blue, yellow, red and purple colors are absorbed. Thus the plants would not be able to use the green light for the process of photosynthesis. This would help in limiting the growth of the duckweeds.