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 these is a structure that is present in all organisms?  
 (A) a tissue (B) a cell (C) a stomach (D) a brain
[EX A]: B

[EX Q]: Parents with freckles often have children with freckles. This occurs because  
 (A) freckles develop from light. (B) certain foods cause freckles. (C) certain habits cause freckles. (D) freckles are an inherited trait.
[EX A]: D

[EX Q]: Which of the following is the main reason water at the surface of the ocean is warmer than water at the bottom of the ocean?  
 (A) Water at the bottom of the ocean contains more dissolved solids. (B) Water at the surface of the ocean absorbs more energy from the Sun. (C) Friction is created by fast moving currents at the surface of the ocean. (D) Wave action transfers heat from the bottom of the ocean to the surface.
[EX A]:
B