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]: ride : horse. compose : ?
[A]: symphony


[Q]: swat : fly. brush : ?
[A]: hair


[Q]: drink : water. write : ?
[A]:
letter