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.

Some types of bacteria can only live where oxygen is not present. These bacteria were well adapted to life on Earth over 2 billion years ago. Which of the following changes caused many of these bacteria to become extinct?  
 (A) the slow movement of tectonic plates (B) the varying temperatures of each season (C) an increase in volcanic activity under the oceans (D) an increase in the number of photosynthetic organisms
D

At what time on a sunny day will the shadow of the school's flagpole be the shortest?  
 (A) sunrise (B) noon (C) mid-afternoon (D) sunset
B

Which sequence correctly shows the levels of organization for structure and function in a human?  
 (A) cell -> tissue -> organ -> organ system (B) organ system -> cell -> tissue -> organ (C) tissue -> organ -> organ system -> cell (D) cell -> organ -> tissue -> organ system

A