阅读下列短文,从所给的四个选项中选出最佳答案. A young man once
题型：完形填空
问题：
阅读下列短文,从所给的四个选项中选出最佳答案. A young man once asked Albert Einstein, the great scientist, 1 the secret of success（成功） is. The scientist told him that the secret of success is 2 work. A few days later the young man asked him the same question again. Einstein was very 3 . He did not say 4 , but wrote 5 words on a piece of paper and handed it 6 the young man. The young man looked at the piece of paper. 7 it was written: A=X+Y+Z. “What does this mean?” asked the young man. “A means success,” explained the old scientist. “X stands for（代表） hard work, Y stands for good methods（方法）, and Z…, Z means stopping 8 and getting down to work.”
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，正电荷
，正电荷
，负电荷
，负电荷