You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

[EX Q]: A delta can be seen from the air at the mouth of the Mississippi River. This delta was formed by
(A) erosion. (B) weathering. (C) conservation of soil. (D) deposition of sediment.
[EX A]: D

[EX Q]: When nitrogen-rich runoff from farms enters a nearby farm, it causes abundant growth of algal mat on the pond surface. As a result, underwater plants in the pond begin to die. Identify the limiting factor that is most responsible for causing the underwater plants to die.
(A) oxygen (B) sunlight (C) nitrogen (D) carbon dioxide
[EX A]: B

[EX Q]: Organisms that consume wastes to obtain the nutrients they need to survive are classified as
(A) decomposers (B) herbivores (C) predators (D) producers
[EX A]:
A