So far:
January 2009 - Age
June 2009 - Gender
January 2010 - Ethnicity
June 2010 - Gender
January 2011 - Gender
June 2011 - Class and Status
January 2012 - Sexuality
June 2012 - Ability/Disability
January 2013 - Age
June 2013 - Regional Identity
June 2014 - Class and Status (it's not online yet, but this is the paper I sat last year)
So I would bank on a question being on sexuality, ethnicty or ability/disability.