The correct answer is A. Protecting nature for its own sake.
Deep ecology is a philosophy of environmentalism that emphasizes the intrinsic value of nature and the importance of living in harmony with the natural world. It argues that humans are not separate from nature, but are part of it, and that we have a moral obligation to protect the environment for its own sake, not just for our own benefit.
Option B, ecology of deep sea, is incorrect because deep ecology is not a specific type of ecology. It is a philosophy that can be applied to all aspects of environmentalism.
Option C, ecology of forest, is incorrect because deep ecology is not specifically concerned with forests. It is concerned with all of nature.
Option D, ecology of caves, is incorrect because deep ecology is not specifically concerned with caves. It is concerned with all of nature.