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: A DNA strand contains codons, which consist of a sequence of three nucleotides. Which best describes the importance of codons found in the sequence of DNA?
(A) They contain the code for messenger RNA. (B) They signal the start of mitotic cell division. (C) They ensure proper replication of the genetic code. (D) They are used to assemble amino acids for protein synthesis.

Answer: D

Question: Sara tums on a flashlight and holds an object up to the light. How will she be able to tell if the object is opaque?
(A) No light will shine through. (B) Some light will be reflected. (C) The light will bend at an angle. (D) Light will shine clearly through.

Answer: A

Question: Why is it winter in North America when it is summer in South America?
(A) The south is always warmer than the north. (B) There is less land than water in the south. (C) North America receives less direct sunlight during the winter. (D) When it is December in North America, it is June in South America.

Answer:
C