The mass of living material at a trophic level at a particular time is called
Net primary productivity.
Gross primary productivity.
The correct option is C Standing crop.
Standing crop is the total amount of living material in a specified population at a particular time, expressed as biomass (standing biomass) or its equivalent in terms of energy. The standing crop may vary at different times of the year; for example, in a population of deciduous trees between summer and winter.
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.