Here is an example

来源: 于 2011-07-27 18:45:45 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

The following link is an example for I-485 interfiling including the sample letter. You may just refer to this sample letter for your draft of response to the RFE though this example is somewhat different from your case:

http://bbs.wenxuecity.com/immigration/541265.html