Some students are performing a hydrobiology project on a creek. they obtained the gpp value as 7 mg/l and the r value as 3 mg/l. what could be the npp for the creek water?

The answer is C, with 4mg/l. Because 7-3, equals four and secondly, just took the test and the answer was four.

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

thats not even an aswer choice