Select the most appropriate option to fill in the blank.

Tickets for the event are available ______ the door; there is no advance booking.

at

The most appropriate option to fill in the blank is at.

The phrase "available at the door" means that the tickets can be purchased at the entrance to the event venue. This is the most common way to purchase tickets for events that do not have advance booking.

The other options are not as appropriate in this context.

• In the door could be interpreted as meaning that the tickets are inside the door, which is not the case.
• Of the door is not grammatically correct.
• To the door could be interpreted as meaning that the tickets are being taken to the door, which is also not the case.