PDM -> Critical Path ?



Want to ask for those using FasTrack pmp exam. I've found a question in time that is calculating the duration for the critial path but they are adding more (1) I didn't get why n how.


I can't upload a photo of the AON diagram, however they are saying that the critical path is something like 

A ->C->D->G->H->J, where G and H have no actual connection or arrow between them?!!! can this be, please clarify. thanks,

 Some one assist me in this please.