Appology
Dear Mr.  Ms,

We are sorry we cannot send you immediately the catalogue and price list for which you asked in your letter of March 10. Supplies are expected from the printers in two weeks and as soon as we receive them, we will send you a copy.

Yours faithfully

道歉

尊敬的先生小姐，

对三月十日来信所要目录和价格单，很抱歉不能马上寄去。印刷商两周后供货，一旦收到，我们将给您寄去一份。

您诚挚的

Explanation
Dear Mr.  Ms,

I was very concerned when I received your letter of yesterday complaining that the central heating system in your new house had not been completed by the date promised.

On referring to our earlier correspondence,I find that I had mistaken the date for completion. The fault is entirely mine and I deeply regret that it should have occurred.

I realize the inconvenience our oversight must be causing you and will do everything possible to avoid any further delay. I have already given instructions for the work to have priority and the engineers working on the job to be placed on overtime. These arrangements should see the installation completed by next weekend.

Yours faithfully

解释
尊敬的先生小姐，

昨天收到你的来信，抱怨你新家的中央加热系统未按规定时间装好，对此我非常关心。参考较早的通信，我发现我搞错了完成日期。错误完全是我的，对此我非常抱歉。

认识到我们的疏忽给你造成的不便，我们将竭尽全力避免再耽搁。我已指示这项工作优先做并让工程人员加班。这样安排会于下周完成安装。

你诚挚的