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       SHANGHAI-Famed Chinese scientist Qian Weichang died here on Friday morning, saddening millions of his countrymen.        He was 98.        Qian, a pioneer in mechanics and applied mathematics in modern China, was one of the three famous Qians in China's science and technology field. He was well known alongside Qian Xuesen, the father of China's space program, and Qian Sanqiang, a nuclear physicist who oversaw the development of China's nuclear program.        Wu Shuqing, former president of Peking University, said Qian was an internationally well-known scholar wh3．下列叙述中正确的是（　　）A．SiO2晶体中每个硅原子与两个氧原子以共价键相结合B．金属晶体的熔点都比分子晶体的熔点高C．金刚石的晶胞中含有4个碳原子D．NaCl晶体中与每个Na+距离相等且最近的Na+共有12个