TASK DEFINITION: You are given a science question (hard-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.
PROBLEM: Which of the following is a similarity 20 between x-ray waves and sound waves?  
 (A) Both transfer energy. (B) Both require a vacuum. (C) Both have the same speed. (D) Both have the same frequency.

SOLUTION: A

PROBLEM: Which example best illustrates an action-at-a-distance force?  
 (A) lifting a box (B) an apple falling (C) pulling a nail out of wood (D) a car moving along a flat surface

SOLUTION: B

PROBLEM: Which is a fact about penguins?  
 (A) Penguins can live in climates with freezing temperatures. (B) Penguins are fierce competitors. (C) Penguins are some of the most beautiful birds. (D) Penguins make great pets.

SOLUTION:
A