Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: In 2004 the Hubble space telescope captured images of distant star clusters, each containing about a million stars. These star clusters were most likely part of which structure?
a galaxy
The Local Group of Galaxies.