What leads to the ionization of nebulae in high star-forming regions?
Group of answer choices
High-energy radiation from the young and hot stars in this region is capable of ionizing the gas.
Planetary nebula activity, resulting from the expulsion of a star's outer layers, is the primary cause of ionization in high star-forming regions.
Cosmic dust absorption in the interstellar medium is the main factor responsible for ionizing nebulae in high star-forming regions.
Gravitational collapse, a fundamental process in star formation, directly leads to the ionization of nebulae.