evidence issue

Hi Friends,

my I-485 is in the processing, I just got a letter from USCIS which asks me to submit an explanation as to why the address of mine and my wife are different since I have moved to another city to work after I submitted I-485, but my wife still works in the same place as where we submitted I-485 and she is applicant, I am dependent. Did somebody have same experience before? how can I properly response this request? and do I have to submit a employment letter?

Thank you for your help!