Conservation usually refers to the limited and proper use of a resource in order to prevent it from getting exploited or damaged. One example is the conservation of resources by implementing sustainable development methods for future generations.
Recycling and the use of solar energy are two examples of conservation. It is because recycling helps in reusing any resource by using alternate methods, whereby the waste produced from one resource is useful for another purpose. Solar energy is one of the most commonly used resources as the sun is the main producer of energy, which is renewable and does not produce any harmful gases that can affect the environment.
Hence, the correct answer is option (D)- which includes both (A) and (B).