The correct answer is A. There would be an increase in dead matter and a lack of nutrients in the soil.
Step-by-step explanation:
Decomposers such as mushrooms are organisms that break apart dead matter, this is the last step or final link in a food web because decomposers break apart any death organism including top predators and they return the nutrients taken by these to the soil, which is necessary for producers or plants to exists. Due to this, if decomposers were removed dead matter would increase as this would not be broken apart by decomposers; and there would be fewer nutrients returning to the soil which would affect producers such as plants.