Explanation

Black polythene absorbs solar radiation and heats the soil, while white or clear mulch reflects light and keeps the soil cooler. Polythene generally reduces evaporation but black is specifically used for temperature control in many contexts, though typically it increases temperature. Wait, let me double check. Black plastic mulch warms the soil. White plastic mulch reflects sunlight and cools the soil. Clear plastic mulch also warms the soil. So white polythene reduces soil temperature relative to black or bare soil in hot conditions. However, sometimes 'polythene' implies clear/black in general contexts. Let's verify standard agricultural MCQs. Often, white mulch is cited for cooling. But some sources say plastic mulch generally increases soil temp compared to organic. The question asks which reduces soil temperature. White polythene reflects radiation, thus reducing soil temperature compared to black or bare soil. So B is likely correct. Current answer A is too vague and usually plastic mulches are associated with warming except white. I will suggest B.