The correct option is C Sunlight
Minerals and fossil fuels like coal and petroleum are exhaustible i.e., they will get depleted through use. Even though water is abundant, we need to conserve it as it is not available everywhere and ground water takes time to replenish. Many places in the world face a shortage of water. In contrast, sunlight is abundant and available throughout the Earth. We will never 'run out of' sunlight. Hence, it need not be conserved.