Two analogies that relate places/locations to the associated travel mode is given in the form "A : B. C : ?". "A : B" relates place A to travel mode B. Your task is to replace the question mark (?) with the appropriate travel mode for the given place C, following the "A : B" relation.

hotel : taxi. mars : ?
spaceship

mall : bus. hospital : ?
ambulance

restaurant : taxi. washington : ?

train