Not only a RFE, but also a long long time waiting

if CIS officer doubt your marriage certification is a real one,they will transfer it to US consulate in China, will spend a long time to get response.
If you attach a notary from Chinese Notary Office,even CIS officer doubt it, just ask you to do a reconfirmation (認證) in Chinese Embassy or Consulate General in USA,can save a lot of time.