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]: What is the name of the product formed from the reaction shown below? 4Fe(III) + 3O_{2} -> 2Fe_{2}O_{3}  
 (A) iron (II) oxide (B) iron (III) oxide (C) oxygen ferrite (D) diferrous trioxide
[EX A]: B

[EX Q]: A student notices a paw print while walking in a park. The paw print could be considered a fossil if the print was in ___.  
 (A) rock (B) topsoil (C) thick mud (D) loose sand
[EX A]: A

[EX Q]: Secondary pollutants are produced in the environment by chemical reactions involving primary or emitted chemicals. Which of the following is a secondary pollutant?  
 (A) carbon monoxide (CO) (B) nitrogen oxide (NO) (C) methane (CH_{4}) (D) ozone (O_{3})
[EX A]:
D