题目内容：
根据以下内容，回答题。Dear New Resident,
Let us be the first to welcome you to lovely New Westford City! We're sure you'll find it to be a wonderful place to own a home.
As a very special welcome from New Westford Carpet Cleaners, please find the enclosed gift certificate, which entitles you to 15% off the regular rate of any one of our services. Whether you require a complete shampoo and steam cleaning for your wall-to-wall carpeting or just a simple stain removal for your furniture fabric, you can count not on us to provide quick, professional ser-vice.
We hope you give us the opportunity to show you why we're the number-one cleaning opera-tion in New Westford City!
Sincerely,
Peter Cavarretta
President, New Westford Carpet Cleaners
What is the main purpose of the letter? A．To inform residents about public transportation
B．To promote a local business
C．To attract tourists to the city
D．To announce a special real estate offer
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