The definition given below describes which of the following?
"The mass of living material at a trophic level at a particular time".

Standing crop is the total amount of living material in a specified population at a particular time, generally expressed as biomass. The standing crop may show variation at different times of the year.

Net Primary Productivity (NPP) is the rate at which plants incorporate atmospheric carbon through photosynthesis.

Gross primary production (GPP) is the rate at which an ecosystem's producers capture and store a given amount of chemical energy as biomass in a given length of time.