Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
The emission spectrum of hydrogen is discontinuous. The spectrum is made up of discrete lines representing transitions of the hydrogen electron between specific energy levels within the atom.


Question: The spectrum is made up of discrete lines representing transitions of the hydrogen electron between specific energy levels within what?
the atom
The atom.