The correct answer is: A. supported rail joint.
A supported rail joint is a type of rail joint where the rail ends rest on a joint sleeper. The joint sleeper is a special type of sleeper that is designed to support the rail ends and provide a smooth transition between the two rails. Supported rail joints are typically used in areas where there is a lot of traffic, as they provide a more stable and durable joint than other types of rail joints.
A suspended rail joint is a type of rail joint where the rail ends are suspended from a beam or other support. Suspended rail joints are typically used in areas where there is a lot of vibration, as they allow the rails to move independently of each other and reduce the amount of vibration that is transmitted to the track.
A bridge joint is a type of rail joint that is used to connect two rails that cross over a bridge. Bridge joints are typically made of steel or concrete and are designed to withstand the weight of the train and the forces of the wind and the weather.
A base joint is a type of rail joint that is used to connect two rails that are at different levels. Base joints are typically made of concrete or asphalt and are designed to provide a smooth transition between the two rails.