You could use the show/hide rules to accomplish this.
For Item A, a particular response is selected. This response triggers the showing of Item B, based on the show/hide rules you have constructed. If Item A has three possibilities, you would construct three possible Item B next questions, only one of which would actually be shown, depending on the selection in Item A.
See the tutorial here: http://forums.adobe.com/thread/869959
Hope that helps.