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行车设备维修施工管理规定
在关系模式中，实现“关系中不允许出现相同的元组”的约束是（）约束。
A、候选键
B、主键
C、键
D、外键
下面题基于学生-课程数据库中的三个基本表：。
A、πsname(σcname=‘MySQL’(s×sc×c))
B、πsname(σcname=‘MySQL’(s∞sc∞c))
C、πsname(σcname=‘MySQL’⊥sc.sno=s.sno⊥sc.cno=c.cno (s×sc×c))
D、πsname(σcname=‘MySQL’⊥sc.sno=s.sno (s×sc×c))
更新数据表中的记录用（）。
A、DELETE
B、ALTRE
C、UPDATE
D、SELECT
It has become an important tool with many advantages.
A、这已经成为重要工具，但优势不多。
B、这已经具有很多优势，成为重要工具。
C、这已经成为具有许多优势的重要工具。
_____pity you missed the lecture again!
A、What
B、What a
C、How
Do not think that you are helping others who are not fortunate, but think of it as a/an _______.
A、exchange
B、bargain
C、trade
-Mom, I have got the first prize! -_____________
A、Really? It is not true.
B、Oh, don’t say that.
C、Great! I am so proud of you!
But I have no idea _________ they would like to put up on their walls.
A、that
B、what
C、which
We＿ all try our best to do some volunteer work.
A、would
B、could
C、should
My volunteer work helps me _______.
A、grow up
B、check up
C、cheer up
My volunteering at an animal shelter is neither connected to my studies nor to my career interests.
A、我在动物收容所做义工，它既与我的学习无关，也与我的职业兴趣无关。
B、我在动物收容所做义工，它和我的学习无关，和我的职业兴趣有关。
C、我在动物收容所做义工，它和我的学习有关，和我的职业兴趣无关。
A car accident can happen ____ you least expect it.
A、when
B、but
C、otherwise
Why not ______ yourself with other friends together?
A、like
B、enjoy
C、appreciate
-Wow! This is great! -_____________________
A、So do I.
B、Don’t mention it.
C、I agree with you. You are right.
I like the idea _______ we go shopping together.
A、that
B、what
C、which
A、候选键
B、主键
C、键
D、外键
下面题基于学生-课程数据库中的三个基本表：。
A、πsname(σcname=‘MySQL’(s×sc×c))
B、πsname(σcname=‘MySQL’(s∞sc∞c))
C、πsname(σcname=‘MySQL’⊥sc.sno=s.sno⊥sc.cno=c.cno (s×sc×c))
D、πsname(σcname=‘MySQL’⊥sc.sno=s.sno (s×sc×c))
更新数据表中的记录用（）。
A、DELETE
B、ALTRE
C、UPDATE
D、SELECT
It has become an important tool with many advantages.
A、这已经成为重要工具，但优势不多。
B、这已经具有很多优势，成为重要工具。
C、这已经成为具有许多优势的重要工具。
_____pity you missed the lecture again!
A、What
B、What a
C、How
Do not think that you are helping others who are not fortunate, but think of it as a/an _______.
A、exchange
B、bargain
C、trade
-Mom, I have got the first prize! -_____________
A、Really? It is not true.
B、Oh, don’t say that.
C、Great! I am so proud of you!
But I have no idea _________ they would like to put up on their walls.
A、that
B、what
C、which
We＿ all try our best to do some volunteer work.
A、would
B、could
C、should
My volunteer work helps me _______.
A、grow up
B、check up
C、cheer up
My volunteering at an animal shelter is neither connected to my studies nor to my career interests.
A、我在动物收容所做义工，它既与我的学习无关，也与我的职业兴趣无关。
B、我在动物收容所做义工，它和我的学习无关，和我的职业兴趣有关。
C、我在动物收容所做义工，它和我的学习有关，和我的职业兴趣无关。
A car accident can happen ____ you least expect it.
A、when
B、but
C、otherwise
Why not ______ yourself with other friends together?
A、like
B、enjoy
C、appreciate
-Wow! This is great! -_____________________
A、So do I.
B、Don’t mention it.
C、I agree with you. You are right.
I like the idea _______ we go shopping together.
A、that
B、what
C、which