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A、B、C、D、E、F均为短周期元素.A的原子半径是短周期中最大的,B元素的原子最外层电子数为m,次外层电子数为n,C元素的原子L层电子数为 m+n,M层电子数为m﹣n,D元素与C元素同主族,E元素原子与B元素原子的核外电子数之比为2:1,F的一种原子中,质量数与质子数之差为0.

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    With over 300 years of history, Harvard University, US, welcomed its first-ever Chinese commencement(毕业典礼) speaker. On May 26, He Jiang, a 2016 PhD(博士学位)graduate, gave a speech that stood for the graduate students at commencement. It's one of the highest honors for a Harvard graduate.

    In his speech, he told a story about his childhood. He grew up in a poor village in Hunan. Once a spider bit him on the hand, and his mother had to set his hand on fire to cure him. There were no doctors in the village, and this was the only cure a rural woman knew.

    When he got older, he couldn't help but think about why there wasn't a better cure at that time. And he thought out the answer ---- the unequal distribution of knowledge in the world.

     “Even today we haven't been very successful in bringing knowledge to where it's needed most,” said He. “Even basic life-saving knowledge we can get easily in the modern world is often unavailable in poor areas.” According to the China Children and Teenagers Foundation, there are still around 3 million children in China lacking education, and most of them live in rural areas.

     “One of the biggest problems for rural students is that they lack chances as well as motivation(积极性). It disturbs me that many people in rural areas think studying is useless.” Said He.

    But He Jiang knows how education can change people's lives. “I just hope my experience can give those rural students a bit of encouragement and hope,” said He.