Hi. I think what you're after is known as cascading (or filtered) value lists, i.e. the options offered in field B are dependent on the value selected in Field A. So a search for cascading value lists would bear fruit. You may also want to take a look at this post that I wrote a while ago, which addresses the additional issue of how to elegantly offer ALL options in Field B if NO option is selected in Field A.
Thank you for your help on this. It is greatly appreciated.