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.

[Q]: The students in a class are making a scale model. They need a material that they can easily bend into a circle. Which of the following objects is best for the students to use?  
 (A) copper wire (B) glass rod (C) lead pipe (D) wooden stick
[A]: A


[Q]: Several horses grazed in a fenced area across from a home. On rainy days, soil would wash down a slope and run toward the home. After the horses were moved a few years later, the soil no longer washed down when it rained. What could account for this change?  
 (A) The grass grew and kept the soil intact. (B) The fence kept the soil contained. (C) The soil was completely gone. (D) The amount of rain decreased.
[A]: A


[Q]: Ana is a cross-country runner. After finishing a race she noticed that she felt hot due to the release of thermal energy. Which is the most likely source of the thermal energy?  
 (A) friction from the air (B) heat being absorbed from the sun (C) mechanical energy being absorbed (D) energy conversions occurring in her body
[A]:
D