A does not express a complete thought?

You are absolutely right! The letter "A" by itself does not express a complete thought.

Here's why:

* Words are the building blocks of sentences: Sentences are the units of language that convey complete thoughts. Words need to be combined into a meaningful structure.

* "A" is just a single letter: It lacks the necessary components of a word, let alone a sentence.

To express a complete thought, you need a sentence containing at least a subject and a verb:

* Example: "The dog barked." ("Dog" is the subject, "barked" is the verb).

Let me know if you have any other questions!