Detailed Instructions: You are given a science question (easy-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:A line graph is best used when the measured variable is
(A) changing at a constant rate. (B) nearly equal in several trials. (C) being compared to a control. (D) observed at one point in time.
Solution:
A