Hint: Energy is needed to change a situation or condition that would otherwise exist naturally. Direct Solar energy is the most important form of renewable energy.
Complete Answer: Solar energy is a renewable source of energy, unlike coal and petroleum. Renewable energy is the energy which is collected from natural resources and can be replenished naturally on a human timescale. Renewable energy is the cheapest source of energy and is a pollution-free source. India has developed technology for the production and utilisation of solar energy. In the Bhuj district of Gujarat, it is used for sterilising milk cans.
Direct solar energy is becoming popular in the remote areas where it is used for cooking, space heating, the lighting of homes and streets etc. A solar water heating consists of a flat plate metal collector connected to a metal tubing which connected by a pipe to an insulation tank is placed towards the general direction of the sun. The blackened flat plate has a layer of thermal insulation beneath it. The collector absorbs the solar radiation and transfers the heat to water, with the help of a pump or by gravity is circulated to the insulation tank. The water is stored in the insulated tank for future use.
The abundant sunlight in the semi-arid or coastal areas is used for converting saline water into distilled water through the method of solar distillation. Direct solar energy is also used for drying of animal and agricultural products.
Thus, the correct option is (D) because direct solar energy is also used for water heating, distillation and drying.
Note: India is a tropical country and has enormous possibilities of tapping solar energy. Photovoltaic technology converts sunlight directly into electricity. Solar energy is fast becoming popular in rural and remote areas.