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]: Planting certain crop plants in a field causes a disruption of the natural nitrogen cycle in that field. Which outcome would this disruption most DIRECTLY cause in the field over time?  
 (A) topsoil erodes (B) soil nutrients decrease (C) desert conditions appear (D) atmospheric carbon dioxide increases
[EX A]: B

[EX Q]: Which would be a safe practice to exercise during laboratory investigations?  
 (A) using open flames to heat all materials (B) keeping your cell phone on the laboratory countertop (C) knowing where your instructor/laboratory leader is at all times (D) removing your safety glasses when moving from station to station
[EX A]: C

[EX Q]: Which statement describes the formation of a delta?  
 (A) A large mass of ice and snow accumulates. (B) A mound of sand is built by wind. (C) A low area of land is surrounded by mountains. (D) A mass of sediment is deposited at the mouth of a river.
[EX A]:
D