Albert Einstein (1879--1955) was one of the greatest and most original scientific thinkers of all time.      Born of Jewish parents at Ulm in Germany,he completed his education in Switzerland and got his Ph. D at the University of Zurich. He went to live in the United States in 1933 because of the rise of Nazism  in Germany and Hitler's persecution   of the Jews.      In 1905, while still at Zurich, he published his Special Theory of Relativity, which was based on things everyone may have noticed. If two trains are standing alongside each other and one train starts to move, a person sitting in the train may wonder whether his own train is moving or the other is moving, and before he finds out what is happening, he can see that one train is moving  ly to the other. From this and also from other more complicated facts, Einstein came to the conclusion that all motion is   and that there are really no such things as     motion. Some of the other conclusions he drew are that nothing can go faster than light, and that if something such as a ruler was moving faster and faster it would seem to get shorter and shorter as its speed was near the speed of light. By 1915, Einstein had made his General Theory of Relativity known. He also improved on Newton's theory of gravity. Most of his theories have been tested and found to be true though some may sound strange. For his important work he was awarded the 1921 Nobel Prize for Physics. Einstein added that if something such as a ruler was moving, it would seem to get shorter and shorter  _  .
when it was moving faster and faster because the ruler itself was short because we can't see it clearly because the ruler was broken into pieces
Question: Albert Einstein (1879--1955) was one of the greatest and most original scientific thinkers of all time.      Born of Jewish parents at Ulm in Germany,he completed his education in Switzerland and got his Ph. D at the University of Zurich. He went to live in the United States in 1933 because of the rise of Nazism  in Germany and Hitler's persecution   of the Jews.      In 1905, while still at Zurich, he published his Special Theory of Relativity, which was based on things everyone may have noticed. If two trains are standing alongside each other and one train starts to move, a person sitting in the train may wonder whether his own train is moving or the other is moving, and before he finds out what is happening, he can see that one train is moving  ly to the other. From this and also from other more complicated facts, Einstein came to the conclusion that all motion is   and that there are really no such things as     motion. Some of the other conclusions he drew are that nothing can go faster than light, and that if something such as a ruler was moving faster and faster it would seem to get shorter and shorter as its speed was near the speed of light. By 1915, Einstein had made his General Theory of Relativity known. He also improved on Newton's theory of gravity. Most of his theories have been tested and found to be true though some may sound strange. For his important work he was awarded the 1921 Nobel Prize for Physics. Einstein added that if something such as a ruler was moving, it would seem to get shorter and shorter  _  .
A. when it was moving faster and faster
B. because the ruler itself was short
C. because we can't see it clearly
D. because the ruler was broken into pieces
Answer: