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.

When sodium hydroxide reacts with a copper nitrate solution, the reaction vessel needs to be kept on ice to slow down the reaction. What best describes this reaction?  
 (A) an exothermic reaction that absorbs energy (B) an exothermic reaction that releases energy (C) an endothermic reaction that absorbs energy (D) an endothermic reaction that releases energy
B

Campers shouted toward a canyon wall. What characteristic of sound best explains why the campers heard an echo?  
 (A) Sound waves traveled slowly down the canyon. (B) Sound waves were absorbed by the canyon wall. (C) Sound waves reflected off the canyon wall. (D) Sound waves were refracted around the canyon.
C

In which part of a plant cell does photosynthesis occur?  
 (A) nucleus (B) chloroplast (C) cell membrane (D) cell wall

B