A "combo"~ticket to enter the fair and ride unlimited rides is ＄$$30$$. A``per ride" ticket costs ＄$$12.50$$ to enter and ＄$$5$$ per ride. For a"combo''ticket to cost less than a "per ride" ticket, a person must go on at least  rides. 
选项为:A:$$3$$  B:$$4$$  C:$$6$$  D:$$7$$  请回答其中一个选项.