單項(xiàng)選擇題

設(shè)有教師表Rl和學(xué)生表R2,如下表所示,則R1R2的行數(shù)和列數(shù)分別為()

A.行數(shù)為12,列數(shù)為5
B.行數(shù)為12,列數(shù)為4
C.行數(shù)為4,列數(shù)為4
D.行數(shù)為4,列數(shù)為5
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