The answer would be C. A haploid cell.
Gametes are haploid cells made by meiosis. Male and female gametes fuse together during fertilization and form the diploid zygote.
You would be studying the links between stress and illness.
Scientific methods are very important for experiments and to explore hypothesis.
Without it we wouldnt even know what the moon is or other planets in this galaxy, scientific method is important to explore and learn the beauty of this planet and galaxy