The Discovery of the Cosmic Microwave Background Was Important Because

The discovery of the cosmic microwave background was important because

A) its detection was a major advance in microwave testing.
B) it established a firm center of the universe.
C) it proved that astronomy at radio wavelengths was possible.
D) it showed the universe must be closed, with more than the critical density here.
E) it was experimental verification of a prediction from the Big Bang theory.