The mushrooms picked by $2$ white rabbits in $3$ days will be eaten by $3$ gray rabbits in $4$ days. In how many days will $15$ gray rabbits eat up mushrooms picked by $5$ white rabbits in $6$ days? 
选项为:A:$$1$$  B:$$2$$  C:$$3$$  D:$$4$$  E:$$6$$  请回答其中一个选项.