Factory $$A$$ can assemble $$20$$ televisions per hour and Factory $$B$$ can assemble $$30$$ televisions per hour. With these constant rates, if $$A$$ assembles $$300$$ televisions in a period, how many televisions can $$B$$ assemble within the same period? 
选项为:A:$$300$$  B:$$400$$  C:$$450$$  D:$$600$$  E:$$900$$  请回答其中一个选项.