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【单选题】
设有关系R(A，B，C) 和S(C，D) 。与SQL语句select A,B,D from R,S where R.C=S.C等价的关系代数表达式是A.
σ[R.C=S.C](π[A,B,D](R×S))
B.
π[A,B,D](σ[R，C=S.C](R×S))
C.
σ[R.C=S.C]((π[A，B]R)×(n[D]S))
D.
σ[R,C=S.C](π[(π[A,B]R)×S)
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【单选题】Seldom _____ TV programs during the day. A. they watch B. watch they C. they are watching D. do they watch
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they watch
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watch they
C.
they are watching
D.
do they watch
【单选题】Jack is watching NBA now. It is______. of him to slip out of the classroom to watch the NBA finals during the final season. [ ]
A.
normal
B.
ordinary
C.
common
D.
typical
【单选题】During the watch keeping at sea, at appropriate intervals inspection should be made of ____, auxiliary machinery and steering gear spaces by the duty engineer.
A.
the main propulsion plant
B.
lifesaving jackets
C.
lifeboat engine
D.
state of emergency generator
【多选题】在下列各组酸碱组分中，不属于共轭酸碱对的是
A.
HAc—NaAc
B.
H 3 PO 4 —H 2 PO 4 -
C.
+ NH 3 CH 2 COOH—NH 2 CH 2 COO -
D.
H 2 CO 3 —HCO 3 -
E.
CO 3 2- —H 2 CO 3
【单选题】给定序列{50,72,43,85,75,20,35,45},按表中元素的顺序依次插入,建立一棵二叉排序树以后,查找元素35要进行( )次元素间的比较。
A.
4
B.
5
C.
7
D.
1 0
【单选题】During the watch keeping at sea, the engineer in charge should notify______in the event of any serious occurrence or a situation where he is unsure of the action to take
A.
the master
B.
the chief engineer
C.
the bridge
D.
the company superintendent
【单选题】During the winter sleep, black bears always______.
A.
sleep like other woodland animals
B.
keep their normal temperature
C.
breathe regularly nine times per minute
D.
live on body fat
【简答题】认真观看“砥砺奋进的五年”大型成就展第九展区,从七个方面中选择其中一项(选择哪一项一定要在回答中注明清楚,如我选择1.准确把握时代大势 开启大国外交新征程),具体结合自己的家乡,描述一下这五年家乡在这方面上的变化,需要有图有真相,家乡一定要写详细(如某省某市某县某镇某村某屯某大队)。 具体格式如下:1.我选择的是..........(填哪一项) 2.第九展区主要讲了.......(做简单陈述) 3...
【简答题】根据事务的操作流程,完成下面连线题目。
【单选题】依次插入序列(50,72,43,85,75,20,34,45,65,30)后建立的二叉搜索树中,查找元素30要进行( )次元素间的比较。
A.
4
B.
5
C.
7
D.
10
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