Mary had equal number of green, yellow and red tokens. She used some of those tokens to make a pile. You can see all used tokens in the figure. She still has five tokens which are not on the pile. How many yellow tokens did she have have at the beginning?  insert pic 
选项为:A:$$5$$  B:$$6$$  C:$$7$$  D:$$15$$  E:$$18$$  请回答其中一个选项.