SASMO 2014 P2 Q6  A shop sells sweets where every 3 sweet wrappers can be excanged for one more sweet. Ali has enough money to buy only 7 sweets. What is the biggest number of sweets that he can get from the shop? 
选项为:A:$$7$$  B:$$8$$  C:$$9$$  D:$$10$$  E:$$11$$  请回答其中一个选项.