Select the correct option from the following.

Give scientific reasons: Even though plants are autotrophic,they cannot live alone.

In an aquatic food chain,at which trophic level can a whale be placed?

What will happen to an ecosystem if:
$(a)$ All producers are removed;
$(b)$ All organisms of herbivore level are eliminated; and
$(c)$ All top carnivore population is removed?

Given below are two statements:
Statement $I$: In an ecosystem,there is a unidirectional flow of energy from the sun through producers to consumers.
Statement $II$: Ecosystems are exempted from the $2^{nd}$ law of thermodynamics.
In the light of the above statements,choose the most appropriate answer from the options given below:

The exchange pool in the carbon cycle is: