Which step completes the pollution process shown? a farmer applies excess fertilizer runoff carries nitrogen to a lake ? lake water becomes oxygen depleted

a.) phytoplankton grow rapidly in the lake then die and decompose
b.) bacteria decrease in the lake water
c.) the lake water becomes clearer
d.) fish become diseased

Option A

Explanation:

Excess of nitrogen and phosphorus from farmlands flows along with the surface runoff (due to heavy rainfall) and mixes with nearby or adjoining water body, and then the problem of eutrophication arises. In eutrophication, the productivity of the lake increases due to excess of nutrients and as a result of this large number of phytoplanktons grows in the water body. This over growth of phytoplanktons causes depletion of dissolved oxygen.  

Hence, option A is correct

i am going to guess that it is co2.

correct answer is a. and d.