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【判断题】
设前提: p?r, q?s, pùq. 则r?s是其有效结论。
【单选题】
若关系R和S分别有r和s个属性,分别含有m和n个元组,则R×S( )
【单选题】
若关系R和S分别有r和s个属性,分别含有m和n个元组,则R×S( )
【多选题】
设前提: (púq) ? (rùs), (sút) ?u. 则下面哪些不是其有效的结论:
【多选题】
若“所有S是P”与“所有P是S”均假,则S与P在外延具有()关系或()关系。
【多选题】
设前提: pù?q ? r, p, q ? s, ?s. 则下面哪些是其有效结论:
【单选题】
假设有关系R和S,关系代数表达式R -(R - S)表示的是( )。
【单选题】
假设有关系R和S,关系代数表达式R -(R - S)表示的是( )。
【单选题】
电子排布式1s22s22p63s23p63d44s2违背了
【单选题】
The earth quake left thousands of people in _____ need of medical care.
【单选题】
____ find out what had happened.
①
Not until he woke up did he
②
Not until he woke up he
③
Until he woke up did he
【单选题】
The Anti ---Japanese War____ in 1937 and it ____ eight years.
【单选题】
—Who broke the window ? —Not me. It must have been ____ else.
【单选题】
It was the training that he had as a young man ____made him such a good engineer.
【单选题】
Eeveryone is working harder and living a happier life now, _________ ?
【单选题】
Most people come to realize that it is about time the government ____ further measures to control the population.
【单选题】
--_______ I put my coat here ?-- Sorry, you ________ .
【单选题】
My____ brother is five years ____ than I.
【单选题】
By the end of last month, she _____ over five hundred letters of congratulation from different parts of the world.