In something under half an hour there was a knock at the door.
there be句型可以在句中?
in something under都是副词?
there be结构当然没必要一定是句子的开始。
如At that moment there was a knock on the door, and Sam came in.
你的句子我不作分析,我建议学习找一些一眼看上去就正常的句子。有些句子虽然七分析八分析下来也是对的,但费劲的句子为什么要拿来作例句?