This theory lost its appeal when astronomers discovered quasars and cosmic background radiation. a: oscillating universe theory b: inflation theory c: steady state theory d: big bang theory

Hi!

The answer would be B. Steady state theory.

The steady state theory was a perspective that asserted that despite the universe does not evolve or change, maintaining a constant density. It did acknowledge that stars died, and that new ones were born -but at an equal rate so that the newly formed stars were practically replacing the stars that died out. The steady state theory conclusively stated that the density of the universe had always and would remain unchanged over time.

This theory lost it's appeal due to many reasons, the first of evidences against it surfacing in 1960's. The first was the discovery of quasars which are gigantic black holes that emit massive amounts of energy and are billions of light years away, which means that they depict how the universe seemed like billions of years ago. This offered a comparison of  the universe back then and now, establishing that the structure of the universe had indeed changed.

Cosmic background radiation was a proof against steady state theory, as these radiations were described to have come from multiple small sources by the supporters of steady state theory; however, cosmic background radiation were observed to be uniform in their spread and density, confirming the had a single source, and this supports the big bang theory.

Hope this helps!