What can you serve, but never eat?

What is always in front of you but can’t be seen?

Do you know of a place where the wind blows south and then suddenly shifts direction towards the north?

What number when divided in half becomes zero?

If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

Count The number of F's in the paragraph below:

"FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS"

What can you hold in your right hand, but never in your left hand?

John went to a parrot shop in Mexico, and the parrot owner told him that his parrot is so unique that he repeats everything he hears. John got excited and immediately bought the parrot. John went home and spoke many words, but the parrot does not repeat anything.
He went again to the parrot shop and complaint to the shopkeeper, but the shopkeeper never lied. Explain?

Solve the following series:
AZ, GT, MN, __, YB