Adrian has two ribbons of length $$12 \rm{cm}$$ and $$30 \rm{cm}$$. He cuts each ribbon into shorter pieces of equal length. Every shorter piece from both ribbons is of the same length. What is the greatest length of each shorter piece? 
选项为:A:$$2$$  B:$$3$$  C:$$4$$  D:$$12$$  E:None of the above  请回答其中一个选项.