阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。

     One morning，I was waiting at the bus stop，worried about ____（be） late for school.There were many people waiting at the bus stop，____ some of them looked very anxious and____（disappoint）．When the bus finally came，we all hurried on board.I got a place next ____the window，so I had a good view of the sidewalk.A boy on a bike ____（catch） my attention.He was riding beside the bus and waving his arms.I heard a passenger behind me shouting to the driver，but he refused ____（stop） until we reached the next stop.Still，the boy kept ____（ride）．He was carrying something over his shoulder and shouting.Finally，when we came to the next stop，the boy ran up to the door of the bus.I heard an excited conversation.Then the driver stood up and asked，“____ anyone lose a suitcase at the last stop？”A woman on the bus shouted，“Oh dear！It's____（I）．”She pushed her way to the driver and took the suitcase thankfully.Everyone on the bus began talking about what the boy had done，and the crowd of strangers____（sudden） became friendly to one another.

东北地区的房屋多有双层窗户，房内或以炕代床，或者有地炉火墙；南方的房屋上比较注重通风透气，这种差别是由于(     )