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 these activities is used to conserve water?  
 (A) planting crops that survive in droughts (B) running water while brushing teeth (C) washing vehicles frequently (D) watering grass after a rainfall

SOLUTION: A

PROBLEM: A human CANNOT survive the loss of which of the following?  
 (A) The appendix (B) The liver (C) A lung (D) A kidney

SOLUTION: B

PROBLEM: Which statement is an opinion about the element copper?  
 (A) Copper is a good conductor of electricity. (B) Copper mixed with silver is expensive. (C) Copper can be pounded into many shapes. (D) Copper is an excellent conductor of heat.

SOLUTION:
B