David takes 30 seconds to climb from the first floor to the third floor. How many seconds will it take him to climb from the third floor to the sixth floor? 
选项为:A:$$30\rm{ seconds}$$  B:$$35\rm{ seconds}$$  C:$$40\rm{ seconds}$$  D:$$45\rm{seconds}$$  E:$$50\rm{seconds}$$  请回答其中一个选项.