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.

Which of these tools is best for recording observations outdoors?  
 (A) a ruler (B) a graph (C) a notebook (D) a calculator
C

When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide
D

The list below gives some symptoms of people with the common cold. Symptoms of the Common Cold stuffy nose low fever sore throat cough Which body system is most affected by the common cold?  
 (A) Nervous (B) Digestive (C) Circulatory (D) Respiratory

D