如何邮件婉拒老师给的offer

Dear Professor,

I am very sorry to tell you that, after very serious consideration, I decide to withdraw the application for your Phd program. Meanwhile, I accept another offer.

Since a Phd research is not easy, I have to choose the thesis that I am most interested in. And unfortunately, there is only one I can choose. That is, absolutely, a pity, and maybe wrong to you. But I have to be honest to myself, and follow my own heart.  

Here, I thank you a million for your favorable consideration for me, and your valuable time dedicated to help me prepare the application materials. You are really nice people. To exchange with you is just enjoyable. I sincerely hope it will be not the end of our interactions. I wish.

Now I am not sure is there any administrative procedure should be followed to withdraw my application? Please keep me posed.

Best regards,
XXX

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