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!

The students can’t go out  ____ （在上学日的晚上）。

为验证人体呼出气体中含有较多的二氧化碳，先向甲、乙两试管内分别注入澄清透明的石灰水，再向甲试管的石灰水中通入空气，向乙试管的石灰水中吹入呼出气，结果是（　　）