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.

Ex Input:
After a star runs out of most of its hydrogen fuel, it becomes hotter and more luminous. What stage does this represent in the life cycle of a star?  
 (A) quasar (B) protostar (C) red giant (D) white dwarf

Ex Output:
C


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

Ex Output:
C


Ex Input:
After nitrogen becomes part of the lithosphere, what is the next change that nitrogen will undergo?  
 (A) used as a nutrient by plants (B) fixed by bacteria in the soil (C) converted into oxygen (D) absorbed into the atmosphere by lightning

Ex Output:

B