You want to know the prices of some air conditioners.
We are interested in your air conditioner and we would like to know the prices of some air conditioners.
You saw an advertisement in the newspaper yesterday and you want further information.
We are writing in connection with the advertisement in the newspaper yesterday.
You want to know if the company you are writing to organizes holidays to Africa.
We are writing to inquire about the holidays to Africa that your company organizes.
A company wrote to you on 23 July. They wanted to know if you sell photocopiers.
Thank you for your letter of 23 July, asking if we sell photocopiers.
A man wrote to you on 18 December. He wanted employment with your company. He also sent his curriculum vitae.
We have received your letter of 18 December, enclosing your curriculum vitae.
A company sent you a fax on 3 June. They wanted to know if you were going to the marketing conference in London.
Thank you for your fax of 3 June, asking if I was going to the marketing conference in London.
A woman telephoned you this morning. She wanted to know if her order No. 599 had arrived.
Thank you for your telephone call this morning concerning the order No. 599.
注：引入主题的句子可以被写在信件的开头，但with regard to 不能用于信件的开头。
环境：(how would you start a letter about each of the following?)
an invoice (No. 679) for a photocopier
With reference to Invoice No. 679, we regret to tell you that the product arrived in bad condition.
a meeting you had with the addressee on Jan. 16th
Further to the meeting on 16 January, I am delighted to tell you that we are now able to give you a special offer for our Peach Series computer.
an advertisement in the times newspaper
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上海市外来从业人员综合保险暂行办法上海市人民政府令第123号 第一条 （目的）为了保障外来从业人员的合法权益，规范单位用工行为，维护本市劳动力市场秩序，根据本市实际，制订本办法。 第二条 （含义）本...（查看全文）