Deal with my MS Word automation program

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C#

When I try to deal with my MS Word automation program in the following steps:
1,Start a winword.exe process by new Word.ApplicationClass();
2,Open a .doc document;
3,Do something with the opened document.
4,Close the document,and go to step2.

And I find that the memory taken by winword.exe increases and releases little even if after the doc.Close( , , ) as the program executes as steps above.That's a problem!how can i deal with it.thank you!