Why does plastic flow only occur below 15 meters of ice

It takes the weight of that much ice to cause the plastic flow.

Ithink i might know wait one second let me serve

Answer is b)eutrophication occurs when excess nutrients are present in aquatic ecosystems, resulting in the increased production of plant life and the subsequent decrease in the oxygen levels of the watereutrophication occurs when there are excess nutrients in a body of water. this results in plants having more food and reproducing  more, sometimes leading to more aquatic animal life as well. ultimately, this can reduce the oxygen level in the ecosystem.