Some Aquatic Invertebrates Such as Insects and Snails Feed on Biofilms

Some aquatic invertebrates such as insects and snails feed on biofilms. Scientists that study metal-contaminated streams have documented that some biofilms in stream environments absorb zinc from stream water during daylight hours and release the zinc into the stream during the night. What might the scientists hypothesize about zinc concentration in the stream?

A) The highest zinc concentrations in stream water might occur only during the day.
B) The highest zinc concentrations in stream water might occur only at night.
C) Zinc concentrations in stream water are likely to be similar during the day and at night.