"Just Do It" joke

A class professor was giving a lecture on company slogans and was asking his students if they were familiar with them.

"Joe," he asked, "which company has the slogan, `come fly the friendly skies`?"

Joe answered the correct airline.

"Brenda, can you tell me which company has the slogan, "Don`t leave home without it?"

Brenda answered the correct credit card company with no difficulty.

"Now John, Tell me which company bears the slogan, `Just do it`?"

And John answered, "Mom."