For many years, scientists thought that the universe was static—that it had always existed and been the same, and it was neither expanding nor contracting. Then, in the late 1920s, Edwin Hubble recognized that the shift in light from distant objects toward the red end of the spectrum meant that those objects were moving away from Earth. The best explanation for these observations was that the universe was not static but was expanding. More recent observations, such as cosmic background radiation, are also better explained by an expanding universe rather than a static universe. What aspect of scientific methodology best explains the replacement of the static universe theory with the expanding universe theory? A Science and its methods are always improving. Scientists needed newer, more sensitive instruments to detect the slow expansion of the universe.

B Hubble’s observations were extremely popular with the public, leading to overwhelming support for the new theory.

C The new theory explained Hubble’s observations, and it was tested and supported by additional observations. The theory was accepted because it was the most powerful explanation available for many observations.

D The natural progression of science is that all theories are eventually replaced by new theories until one is established as law