Questions

A biosphere is the sum of all the ecosystems established on planet Earth.

An ecosystem is an area in which the plants and animals all interact to create a living environment. Therefore ecosystem is a smaller unit of earth, all ecosystems together form the earth.

The Mula-Mutha is a river in India, formed by the confluence of the Mula and Mutha rivers in the city of Pune, which later meets the Bhima River, which itself later meets the Krishna River and finally emptying to the Bay of Bengal.

In the given options, "His stomach rumbled like an approaching train" is an example of Simile.

All the other options are examples of metaphors. 

Simile and Metaphor are both figure of speeches in English which are used for comparing things but the only difference is Simile uses LIKE or AS words in comparing and metaphor directly compares without using any words.