Each Atom in the Periodic Table Has a Unique Set

Multiple Choice

Each atom in the periodic table has a unique set of spectral lines. Which one of the following statements is the best explanation for this observation?

A) Each atom has a dense central nucleus.
B) Electrons in atoms orbit the nucleus.
C) Each atom has a unique set of energy levels that electrons can move between.
D) Electrons in atoms are in constant motion.
E) Each atom is composed of positive and negative charges.