it been a long time.中的“been”,为什么用这个

It's+been++a+long+time.been在这里起什么作用?为什么要用been it had been a long time ,since sb was a girl.这个过去完成式,had bee It -- that he has been ill for a long time 为什么选择A呢 Aseems B what a long time he's been waiting,isn't it?对吗,为什么 Hi Mary It's been a long time .语法填空 找一首歌.歌词里有一句“it s been a too long time” It ___that he has been ill for a long time It has been a long time.Are you ok? it has been a long time. what is up It's a long time since还是It has been a long time since It has been a long It's been a long