【单选题】Chen Yifei(1946-2005),who died in his ________ fifties,was ________ successful artist.
【简答题】改革开放 40年以来,中国高铁已然成为一张有重量的“中国名片”。小明乘坐高铁时看到路旁的树木疾速向后退去,这是以________为参照物。
【简答题】关系代数的运算对象和运算结果为____。
【单选题】Xu Beihong is most known ________ drawing horses________an artist.