Here's why:

* Nebulae are clouds of gas and dust, the raw material for stars.

* Star formation occurs within these nebulae. As the gas and dust collapse under gravity, it heats up and eventually ignites, forming new stars.

* Star clusters are groups of stars that formed from the same nebula at roughly the same time.

So, star-forming regions are areas where the process of star birth is actively happening, and they contain both the stellar nurseries (nebulae) and the newly formed stars.