填空题 2.  The Expanding Universe Theory
    The Big Bang Theory, which posits that the universe began from a single point of incredibly dense matter, is the most widely accepted theory regarding the creation of the universe. According to it, roughly fourteen billion years ago, this matter exploded and expanded to form the present-day universe. This theory is based upon observations of the universe suggesting that it is not static but is instead continually expanding outward.
    For centuries, astronomers believed that the universe was fixed and that Earth was located at its center. By the early twentieth century, the notion that Earth was at the center of the universe had been dispelled, but the static universe theory was still the prevailing model. Even Albert Einstein was a great believer in it. Then, in 1917, he had a revelation. His general theory of relativity did not precisely agree with the static universe model, yet he could not reconcile his strong belief in a static universe with his theories, so he concluded that some unknown force was preventing the universe from expanding. Simultaneously, other astronomers were discovering that Earth and the sun belonged to a large collection of stars they called a galaxy. In 1925, American astronomer Edwin Hubble proved other galaxies existed in addition to Earth's galaxy, which had been dubbed the Milky Way.
    Hubble made further observations that had a profound effect on the static universe theory. In 1929, he realized that the light coming from the galaxies he was observing had a distinctive red shift on the light spectrum. This was due to the Doppler Effect, which makes an object moving away from an observer appear red in color. This meant that the galaxies were moving away from one another and that the universe was expanding outward. There was resistance to Hubble's theory, but Einstein accepted it, and others soon agreed with the expanding universe theory as well. From it, astronomers concluded that if the universe was expanding, then it must have been much smaller at some point. That led to the Big Bang Theory becoming the accepted model for the creation of the universe.
    *static: stationary; unmoving
    *Doppler Effect: a shift in the frequency of the radiation emitted by a source that is moving relative to an observer
    An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas of the passage. Some sentences do not belong because they express ideas that are not presented in the passage or are minor ideas in the passage.
    Thanks to discoveries made by astronomers in the twentieth century, the expanding universe model replaced the static universe model as accepted science,
    ANSWER CHOICES
    ①Edwin Hubble made a discovery that showed that the galaxies in the universe were spreading apart from one another.
    ②The theory of relativity showed Albert Einstein that his notion that the universe was static was incorrect.
    ③Most people throughout history have believed that the universe is static and that Earth can be found at its center.
    ④The belief in the expanding universe model indicated to astronomers that the universe was probably started due to the Big Bang.
    ⑤Albert Einstein and Edwin Hubble worked together to come up with the expanding universe model.
    ⑥The Doppler Effect is what makes an object appear red when it is moving away from another object.