Question

28 edwin hubble’s observations of galaxies supported an idea, which is a key feature of the big bang theory. what is this idea?
the life cycle of stars
the expansion of the universe
the sun as the center of the solar system
the existence of exoplanets

Explanation:

Edwin Hubble's observations of galaxies showed that galaxies are moving away from each other, supporting the idea of the universe's expansion, a key part of the Big Bang theory. The life cycle of stars, Sun as solar system center, and exoplanet existence are not related to Hubble's work on Big Bang - related universe expansion.

Answer:

the expansion of the universe