Listen to the conversation and fill in the blanks. Micheal : Hello, General Computers Technical Support, 1 ? Customer : Hello, this is Li Yang speaking. I have used your General Computers SQL server for quite a while , but I have a question: how can I make an existing column have a 2 ? Micheal : Well, 3 ? What do you mean by a column having a unique constraint? Is it a column with unique values? Customer : Not that. Well, if you are 4 , this question, I have another one. Sometimes when I update a column with unique constrains, it doesn’t work. Is that a 5 or did I do something wrong ? Micheal : Err... I am not very familiar with this problem either, 6 . As a junior support representative, I would advise you to contact our 7 . Would you mind me transferring you now? Customer : If that will solve my problem, 8 . Micheal : 9 for your understanding. Micheal : Hello, General Computers 10 . Can I help you? Bill : Hello, I’d like to speak with Ms.Wang, head of 11 , please? Micheal : May I ask who is calling , please? Bill : My name is Bill Johnson of 12 . I’d like to discuss a project plan with her. Micheal : Thank you, Mr.Johnson. 13 , please..