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.

Pluto was discovered in 1930 and was named the ninth planet. In 2003, an object larger than Pluto was discovered by astronomer Michael Brown. Pluto has been reclassified as a "dwarf" planet. What does this most likely suggest about scientific investigations?  
 (A) Earlier scientists did not use appropriate tools. (B) Pluto should not have been classified as a planet. (C) Classifications change as new evidence is gathered. (D) Review of planetary characteristics should occur every year.
C

Carbon dioxide emissions have increased due to large numbers of automobiles and increased industrialization. Which of the following has been most affected by the increase in carbon dioxide levels?  
 (A) the ability of farmers to plant crops (B) the ability of scientists to study other planets (C) the ability of Earth to continue recycling rocks (D) the ability of Earth to maintain lower temperatures
D

Sound is able to travel faster in solids than in air because the molecules in a solid are  
 (A) closer together than air molecules. (B) more easily moved than air molecules. (C) moving faster than air molecules. (D) larger than air molecules.

A

