Which of the following statements are correct?
$(a)$ Net primary productivity is available biomass for consumption to heterotrophs.
$(b)$ Secondary productivity is defined as the rate of formation of new organic matter by heterotrophs.
$(c)$ The annual net primary productivity of the ocean is greater than that of land.
$(d)$ Warm and moist environment favours decomposition.

• A
  $a, b, c$ and $d$
• B
  $a, b$ and $c$
• C
  $a, b$ and $d$
• D
  $a$ and $c$