Which of the following is used to describe celestial bodies in their early formation stages?

The term used to describe celestial bodies in their early formation stages is nebulae. A nebula is a giant cloud of dust and gas in space and is often considered the birthplace of stars. Within these nebulae, areas of higher density can collapse under gravity, leading to the formation of stars and eventually planets.

Nebulae play a critical role in the lifecycle of stars, serving as the initial material from which stars are born. They contain the essential elements, such as hydrogen and helium, necessary for the formation of new stars. As stars form in these dense regions, some may evolve into star clusters, but it is the nebula that represents the very early stages of celestial creation.

The other options refer to different aspects of celestial structures. For example, star clusters represent groups of stars that have already formed and are bound together by gravity. Gas giants refer to large planets composed mainly of hydrogen and helium, which typically form from the materials found in nebulae but represent a later stage of formation. Stellar nurseries, while closely related to the concept of nebulae, are more commonly associated with specific regions within nebulae where star formation is actively occurring but are not the general term for the formations themselves. Thus, nebulae