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.

[Q]: downtown : subway. mars : ?
[A]: spaceship


[Q]: mall : bus. australia : ?
[A]: airplane


[Q]: store : car. mainland : ?
[A]:
boat