C. Clouds
Explanation - The solar radiation is absorbed by the earth that keeps the atmosphere or the environment of the planet warm. Clouds do not absorb, rather reflects the solar radiation thereby keeping the earth's surface cool.
Thin clouds allows the transmission of the incoming solar radiation towards the earth. Sweater is not involved in maintaining the temperature of the earth. It just keeps our body warm by absorbing solar radiation. Mountains also absorbs solar radiation and helps the plants to grow and animals to live.