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.

What are produced in both the male and female reproductive systems in humans?  
 (A) sperm (B) nutrients (C) fertilized eggs (D) sex cells
D

Spring tides occur during which lunar phases?  
 (A) first quarter and last quarter (B) full moon and new moon (C) when the moon is waxing (D) when the moon is waning
B

Which of the following represents a chemical reaction?  
 (A) a sugar cube dissolving in water. (B) ice cubes forming in a freezer. (C) ice cream melting in a bowl. (D) a cake baking in an oven.

D