The correct answer is A. Habitat destruction.
Habitat destruction is the primary cause of extinction in the world today. It is caused by human activities such as deforestation, mining, and agriculture. When habitats are destroyed, animals lose their homes and food sources. This can lead to starvation, disease, and death.
Climatic changes are also a major threat to wildlife. Climate change can cause changes in temperature, precipitation, and sea level. These changes can disrupt ecosystems and make it difficult for animals to survive.
Non availability of food is not a major cause of extinction. Animals are able to adapt to changes in food availability. However, if food sources are completely eliminated, this can lead to starvation and death.
In conclusion, habitat destruction is the primary cause of extinction in the world today. Climatic changes and non availability of food are also threats to wildlife, but they are not as significant as habitat destruction.