Help for filling IPCC Registration Form

Can any1 tell me wat is d meaning of d different categories or divisions Provided in d IPCC form like ...........

1 . Group I, Group II of  IPCC & A TC  ( all levels ) .

2. Group I and Group II of  IPCC

3.Group I of IPCC  and A TC

4. Group II of  IPCC and ATC

5. Group I of IPCC

6 . Group II of  IPC C

in all d above fields there is a option for wid or widout articles ....wat is d meaning of it??

Will it be correct to regiser for all levels i.e including ATC??