Thanks. The letter also indicated that there needs to be a stament from Foreign Affairs if birth certificate was not available for the time and place. I discussed with a lawyer and he suggested that I go back to the local Security Dapartment and have them write a letter verifying the relationship in their letter head.
-That is called "Family Relationship Certificate" and this can be used as secondary evidence and it is helpful.
I also answered the question about whether my parents are part of communist party "Yes". Do you think that caused a problem?
-It may be a potential problem. But do not do anything at this point unless you receive REF. You may prepare some explanation about the Part member, just in case. Google search to find some sample letters/related information.