关系数据库中的关系运算包含选择、()、连接。
参考答案:投影
—I have learned English so long. But I can't follow the Australian.
—Because English is spoken ______ in different countries. [ ]
A. different
B. differently
C. widely
D. slowly
EHFV其基因RNA可分为L(大)、M(中)、S(小)3个片段,它们分别编码聚合酶膜蛋白和核衣壳蛋白。