Student or Learner
When you want to say something similar to 'I can't stop grinning." using the following sentence, should the article be "a" or "the" ?
I can't wipe a[the] smile off my face.
The indefinite article (a) means you can't wipe any smile off my face, should I have one.
The definite article (the) means you can't wipe the specific smile that currently resides on my face. Definite=specific; indefinite=any. Remember a=any and you won't forget!