I haven't been back to the island是什么时态?为什吗要用been?

I haven't been back to the island是什么时态?为什吗要用been? I haven't been to the mountains Have you___been to Beijing?No,I haven't been the my father hasn't been to Tibet.I haven't been to the Tibet,e I haven't been to Shanghai.( ). having been back for a month,i haven't even got around to un my parents haven't been to shanghai,and i haven't been to sh I haven't been able to be outdoors for so long haven't been 现在完成时句子改错1.I don’t think he’s ever been to the Monkey Island He hasn't been to Beijing.I haven't,either. ----I haven't been to the aquarium before . How about you, T 将句子改成复合句：I am not going to the party.I haven’t been invited.