The correct option is A.
Living organisms depend on their environment to survive, when there are changes in the environment which are not favorable to the living organisms, it will eventually leads to the wiping out of the living organisms. As time goes on and the environment recover, the living organisms that will be found in the new environment are those who will be able to survive in it.
Phytoplankton serves as food for virtually all the organisms living in an aquatic environment. It is a primary food producer and serves as the foundation of aquatic food web. If there is a decline in the amount of phytoplankton, the organisms which feed directly on the plant may reduce significantly as a result of dire competition for food, this in turn will affect the organisms which feed on the dying out organisms and the trend will move in a similar way until it affect all the organisms living in that particular aquatic habitat.
I believe it would be the bronchiole