C. Lengthy and useless.

　　D. Meaningful and perfect.

　　D

　　The majority of physicists once believed that the universe’s expansion was slowing down. In 1998, they were proven completely wrong. Though it flies in the face of scientific theory, the universe is expanding at an ever-increasing rate.

　　One possible explanation is that empty space has a thing called dark energy, which supposedly makes up about three quarters of the universe. Dark energy supposedly very sparsely(稀疏地) exists in such a way that it interacts with other objects only through attracting force. It has a strong negative pressure, which causes it to pull on its surroundings and as a result, pull apart the universe. This neatly explains the universe’s expansion without completely changing our understanding of the universe. Scientists can merely claim that dark energy “should” exist.

　　According to Einstein’s theory of relativity, it is impossible to travel faster than at the speed of light.

　　With this in mind, physicists set out to do the impossible and succeeded. In 2000, scientists in Princeton, New Jersey sent a small pulse(脉冲) of laser light through a vapor made up of gaseous cesium(铯). The pulse traveled so quickly that it was already leaving the vapor-filled chamber as it was still entering, roughly 300 times faster than it would have in a vacuum(真空). Thus, light moved faster than the speed of light.

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