Where is this sign?

Solution:

The sign reads: "ALL PASSENGERS MUST SHOW THEIR TICKET TO THE POLICE BEFORE ENTERING THE PLATFORM." This text indicates a requirement for passengers to present a ticket to the police before accessing a platform. Platforms are typically found at railway stations.

Let's analyze the options:

• A. at a railway station - This is consistent with the presence of platforms and the need to show tickets to police.
• B. at an airport - Airports have terminals and gates, but the term "platform" is not commonly used in this context. Police presence for ticket checks before entering a gate is also less typical than at a railway station.
• C. on a bus - Buses do not have platforms in the same sense as railway stations, and police ticket checks before boarding are uncommon.

The sign's wording strongly suggests a railway environment.

Answer: A at a railway station