Thank you Teacher 8. To clarify, I thought the I-751 filing receipt is the Extension Letter as it states that my US permanent resident status is extended for another year. Please correct me if I am wrong (the only two letters I received since filing my I-751 application are 1)I-751 receipt 2)Biometrics Appointment Letter.)
-Then, just show that letter to the IO and explain you need that green card stamp because the Chinese Customs may not accept the I-751 receipt (extension letter). Based on my understanding, that kind of document can not be used for international travel.