以下（）属于用户定义的完整性约束。A.列值非空B.列值唯一C.CHECK某列的值是否满足要求D.以上都对 A: 列值非空 B: 列值唯一 C: CHECK某列的值是否满足要求 D: 以上都对

He had gone to the reception desk, presumably to ______. A: check on B: check into C: check off D: check out

How to check the quality during production（） A: Check every one. B: Take samples to check it. C: Check it at random.

To show your ticket and get your seat at the airport is to _________. A: check out B: check off C: check in D: check on

What do you have to do before leave hotel（） A: check out B: check in C: check ove D: check on

You must_________at the airport an hour before your plane leaves. A: check in B: check out C: check with D: check over

Hello. I would like to ___________. I booked a room at this hotel online. A: check out B: check in C: check on D: check over

This is the hotel where you’re going to stay. Shall we go to the reception desk and ____________? A: check out B: check over C: check in D: check on

I will be leaving for Shanghai tomorrow . What time should I ? A: check in B: check out C: check

Could you please _______over there in the front office? A. check in B. check off C. check on D. check about