a. Use "a" or "an" with a singular count noun when you haven't let the reader know or are introducing it for the first time. [1. A dinosaur may have consumed as much as a crane bucket full of plant matter everyday.  2. An elephant has almost a two year gestation period, longer than any other mammal in the world.]

 b. "The" precedes a singular count noun that has a specific identity for the reader for the following reasons:

   - The author or writer mentioned it for the reader already.
   - The author or writer identifies the single count noun either just before or after stating it.
   - The author or writer mentions something where only one in the world exists, or is very unique (The George Washington University [[there's only one!]]
   - The author or writer mentions a single count noun that is an institution or item shared across a community or large population. [The computer, the Internet, and the telephone all globally connect people from all over the earth.]