In order to take the OC exam, John spent five weeks practising the OC exercises. In the first week, he practised one set of OC exercises. Since then, he had practised twice as many times each week as the previous before. How many sets of exercises did John practise in total while preparing for the OC exam? 
选项为:A:$$16$$  B:$$63$$  C:$$31$$  D:$$30$$  E:$$21$$  请回答其中一个选项.