Which data is most useful to measure primary productivity in a ...

[penza]

Which data is most useful to measure primary productivity in a terrestrial ecosystem?
A) temperature readings
B) potential evapotranspiration
C) intensity of solar radiation
D) annual precipitation
E) amount of carbon fixed

[plus1]

I recall doing this last year, it's D, bye bye!

[penza]

Thanks for assisting, your answer was right!