题目内容

关系的完整性约束有_,_,_三种。

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自然连接和等值连接的区别和联系。

A rescue worker risked his life saving two tourists who＿＿in the mountains for two days.

A. are trapping
B. have trapped
C. were trapping
D. had been trapped

—Good morning, Mr. lee’s office.—Good morning. I’d like to make an appointment＿＿next Wednesday afternoon.

A. for
B. on
C. in
D. at

—Hi, I’m Peter. Are you new here? I haven’t seen you around？—Hello, Peter. I’m Bob. I just＿＿on Monday.A. start B. have startedC.startedD. had started

A. start
B. have started
C. started
D. had started