You need to look at a Flood Zone map for the property you are interested in getting insurance for and see whether it is in a designated flood zone which uses the letters you mention in your question.
More information can be found online by Googling "FEMA Flood Maps" or www.floodsmart.gov.
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check the flood zone maps or you can pay a flood zone search company to check for you. check FEMA websites for more information.
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You need to look at a flood zone map. Keep in mind, the maps have been, or will be updated, to take into account changes in land caused by hurricane sandy.
If you are in a flood zone of any kind, it is almost certain your mortgage company will require you to get flood insurance.
You should confirm all this with an attorney.