Which of the following are the essential sources for releasing $CO_{2}$ into the atmosphere?
$I.$ Burning of wood
$II.$ Volcanic activity
$III.$ Combustion of organic matter
$IV.$ Fossil fuels
Choose the correct option.

Which one of the following is not a function of an ecosystem?

$A$ food web:

The maximum evolution of oxygen is by which of the following producers of organic matter?

Identify the possible link $A$ in the following food chain.
Plant $\rightarrow$ Insect $\rightarrow$ Frog $\rightarrow$ $A$ $\rightarrow$ Eagle

Read the following statements carefully and answer the question:
$(1)$ Pyramids of number and biomass can be upright or inverted in an ecosystem.
$(2)$ Phosphorus and sulfur are sedimentary cycles.
$(3)$ The largest reservoir of carbon on Earth is found in the oceans.
$(4)$ The structural and functional unit of ecology is the ecosystem.
Which of the above statements are correct?