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?

• A
  $1$ and $2$ only
• B
  $1, 2$ and $3$ only
• C
  $3$ and $4$ only
• D
  All statements are correct