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.

Q: Earth is composed of layers of material with different properties. Which of the following is most likely to be in constant motion?  
 (A) core (B) mantle (C) oceanic crust (D) continental crust

A: B
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Q: A scientist uses angstrom units to measure the distance between two points. The scientist is most likely measuring the distance between two  
 (A) atoms. (B) cities. (C) continents. (D) stars.

A: A
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Q: 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

A:
D
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