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.

mars : spaceship. island : ?
boat

bermuda : airplane. mall : ?
bus

portland : car. mall : ?

bus