Spreading an Infection

    I've made it a habit to smile at people as often as possible, saying some kind words, “hello, thank you, have a nice day”, whatever fits. I have the right situation as I am living in____big city with many, many people.

    I'm doing this for quite a while now, so I've seen all____（kind）of reactions, from people feeling____（threaten） by a friendly word, reacting  ____（angry） or even aggressively, to people____faces lit up with a huge smile and gave me the____（impress） that I've made this moment good for them.

    Today something happened that I hadn't yet experienced: Two people, complete strangers____me, one in the morning, one in the afternoon, whom I passed on the street without ____（smile）at them,____ with a friendly face, looked up from their inner focus, looked at me, started to smile and greeted me friendly while they____（pass）.

    Have I started a “kindness virus”? That would be great! It makes my day, and I'm still smiling. I hope you do too!

长江干流流经的地形区按先后顺序排列正确的是（　　）

①长江中下游平原　　　②青藏高原

③四川盆地　　　　　　④横断山区

一氧化碳使人中毒的原因是一氧化碳与人体血液中的____结合，使血液丧失输____的能力而使人窒息死亡。