Two analogies that signify affordances are given in the form "A : B. C : ?". Affordance is the possibility of an action being done on an object, for example book is an affordance of writing. The phrase "A : B" implies that B is an affordance of A. Your task is to replace the question mark (?) with the appropriate affordance of the given action C, following the "A : B" relation. Your answer should be a single object without further explanation.

[Q]: paint : picture. open : ?
[A]: door


[Q]: write : book. hire : ?
[A]: employee


[Q]: sing : song. ride : ?
[A]:
horse