Which galaxies are generally seen in the earliest (youngest) stages of their lives in observations like the Hubble eXtreme Deep Field?

The answer is based on the fundamental relationship between distance and the age of light from astronomical objects. When observing galaxies that are farthest away, we are actually looking back in time because the light from those galaxies has taken the longest to reach us. Therefore, the farthest galaxies are generally in the earliest stages of their development and thus represent some of the youngest galaxies we can observe.

Observations like those made in the Hubble eXtreme Deep Field focus on capturing light from very distant objects, allowing astronomers to study galaxies as they were in their formative years. As such, these distant galaxies offer unique insights into the conditions and processes that existed in the early universe, including galaxy formation and evolution.

The other options do not correctly identify galaxies in the early stages of their lives. For example, the closest galaxies have light that has traveled a shorter distance; hence, they are more evolved and do not represent the early universe. Galaxies with bright luminous cores typically indicate advanced stages of galaxy evolution, and strong spiral structures are characteristically found in more mature galaxies rather than in the early formative stage.