Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of

a. Weight $\left({\text{gm}}^{–2}\right)$
b. Weight $\left({\text{g}}^{–2}{\text{yr}}^{–1}\right)$
c. Energy $\left({\text{kcal m}}^{–2}\right)$
d. Energy $\left({\text{kcal m}}^{–2}{\text{yr}}^{–1}\right)$

1. $a$ and $b$
2. $b$ and $d$
3. $a$ and $c$
4. $c$ and $d$
   

The correct option is C $a$ and $c$
Primary production

Solar energy from the sun is used by producer organisms like green plants, algae, etc to prepare their own food in the form of organic matter.
Primary production refers to the total amount of organic matter produced, per unit area of an ecosystem, by the producers via the process of photosynthesis.
It is expressed in terms of weight $\left({\text{gm}}^{–2}\right)$ or energy $\left({\text{kcal m}}^{–2}\right)$.