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]: Which of the following forms of energy is released or absorbed in most chemical reactions?      
 (A) light energy (B) electrical energy (C) sound energy (D) heat energy
[EX A]: D

[EX Q]: Marta studied different forms of energy. Which two types of energy travel in waves?  
 (A) light and sound (B) electrical and sound (C) chemical and light (D) chemical and electrical
[EX A]: A

[EX Q]: The growth of which of the following usually occurs first in primary succession on a bare rock?     
 (A) Lichens (B) Grasses (C) Trees (D) Shrubs
[EX A]:
A