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.
Example: Which event can cause a large rock to become soil over time? 
 (A) decaying (B) an earthquake (C) a landslide (D) weathering
Example solution: D
Example explanation: Under the action of heat, cold, rain, wind, and other atmospheric factors, the rock breaks down physically into small fragments that become the parent material of the soil. Also, atmospheric factors change according to weather.

Problem: Students want to test how the temperature changes each day throughout the year. Which of the following does not have to be kept the same during the test?  
 (A) the place where the temperature is measured (B) the thermometer used to take the measurement (C) the person reading the temperature measurement (D) the time of day when the temperature is measured

Solution: C