Hello,While applying SSC cgl2017 form be careful to fill this PREFERENCE ORDER.YOU NEED TO FILL GROUP CODE NOT POST CODE.Let me explain you,•Group code means (A,B,C,D) categories•Post code means (A,C,E,H,%,@,$,..)For suppose if you don't want AAO post or don't have a degree in accounts you must skip Group code:A. Then Your order can be b,c,d or like this…After successfully qualifying tier 1,2,3 you are asked to give POST order according to group that you have given in application form.Hope it helps :-)