An ecosystem is a community made up of living organisms and nonliving components, such as air, water and mineral soil.

A stable ecosystem is an ecosystem, in which, the structure and function remain unaltered over a long period of time.

Oceans are considered to be the most stable ecosystem in nature. They are stable in their chemical composition due to being saline and other features like dissolved oxygen, light, temperature also remain more or less constant. They are deep, continuous and large. Therefore, there are less chances of any prominent change which alter their structure and function. They are well capable of resisting any of the small changes which occur.

Therefore, the correct answer is option A.

Coniferous forests grow in the Himalayan mountain region, where the temperatures are low. Some rare animals that found in Coniferous forest are Snow leopard, Hangul, Himalayan brown bear, Musk deer, Himalayan wolf. Evergreen forests grow in the high rainfall areas of the Western Ghats, North-Eastern India and the Andaman and Nicobar Islands. These forests grow in areas where the monsoon lasts for several months. Some rare animals that found in the Western Ghats are Pigmy Hog, Rhino, Lion-tailed macaque. Thorn forests are found in the semi-arid regions of India. Some rare animals that found in the semiarid forest are Wolf, Bustard, Florican Bustards. Water monitor lizards are found in Mangrove Delta forest.

Nopal plant grows in Mexican desert and turns the barren landforms of Mexico into a picturesque landscape. This is a magical plant of Mexico and is grown by Camémbaro, a farming community. It can be found all over the Mesoamerican region and it is said that it could be an answer to many challenges faced by human beings and would help to combat the problems of climate change. This is a magical plant of Mexico and also known as the prickly pear.

1. Andhra Pradesh: Black buck (Antilope cervicapra)

2. Arunachal Pradesh: Mithun (Bos frontalis)

3. Bihar: Gaur (Bos gaurus)

4. Manipur: Sangai (Cervus eldi eldi)