The correct answer is d. adaptations.
An adaptation is an ability of organisms such as a plants or animals which help them to survive in its changing environment. Adaptation may be due to mutation or genetic change which inherited from generation to generation. Adaption can be structural or behavioral. In a structural adaptation physical part of an organism changes, for example some plants such as cactus adapted to live in desert. In behavioral adaptation action of an organism changes, for example migration of animal from one place to other.