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.

Scientists have studied the specific stages in the life cycle of stars. In which stage do stars spend most of their lifetime?  
 (A) red giant (B) black dwarf (C) white dwarf (D) main sequence
D

Martin is writing a report for science class about how the tilt of Earth affects living organisms. Which subject should Martin include in his report that is directly affected by Earth's tilt?  
 (A) night and day (B) cloud formation (C) phases of the Moon (D) changing of the seasons
D

Which is an example of a different substance being formed?  
 (A) glass breaking (B) metal melting (C) water freezing (D) wood burning

D