They've been waiting here since twenty minutes ago.(为什么加been

They've been waiting here since twenty minutes ago.(为什么加been I've been here since 1976.这句话中been后面为什么不加to I've been here since 1976. 这句话中been后面为什么不加to The film has bugun since 30 minutes ago.这里has后不用加been吗 since,they,been,from,ago,two,here,away,have连词成句 they have been away from here since two years ago同义句 ___ ___ they have been here ___ two hours ago.A.for B.since C.before they have been here since 2000 she has been away since ten minutes ago 对 ten minutes ago 提问 he has been here since five weeks ago. I have been here since three yeas ago 1 We have been here since ten years ago.--------------------