instruction:
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.
question:
In a lab investigation, students use Brand X batteries in a flashlight and Brand Y batteries in a radio. After two hours, the flashlight stops working, but the radio continues to work. As a result, the students conclude that Brand Y batteries last longer. Which statement about the conclusion of the investigation is most accurate?  
 (A) The conclusion is valid because they tested two different brands. (B) The conclusion is invalid because the test had multiple variables. (C) The conclusion is valid because they conducted the investigation in a lab. (D) The conclusion is invalid because the real names of the batteries were hidden.
answer:
B


question:
Which of these is an example of water changing from water vapor to liquid?  
 (A) moisture forming on a mirror when you breathe on it (B) sweat forming on your body when you exercise (C) ice cubes melting when you put them in a warm liquid (D) rivers drying up during a very hot summer
answer:
A


question:
Which of the following would make the best insulator against the flow of electricity?  
 (A) copper wire (B) steel tubing (C) plastic tape (D) aluminum foil
answer:

C