①水蒸气变成液态水   ②生石灰与水反应

③酸碱中和反应         ④Ba（OH）₂•8H₂O与NH₄Cl晶体的反应．

注意：

1）文中不得出现你的真实姓名和学校名称；

2）语言通顺，意思连贯，条理清楚，书写规范；

3）词数 80 左右，邮件的开头和结尾已经给出，不计入总词数。

Dear John,

向你求助。请根据邮件内容写封回信。

Dear Li Hua,

    I will come to Nanjing in July and stay with a Chinese family for a week as an exchange student. To get along well with my host family, should I prepare any gifts? How can I help with the housework? What else should I do?

    Please write back soon.

Yours, John

Dear John,

    I'm glad you will come to China.

    I hope you will enjoy your stay in China.

Yours,

Li Hua

“绿叶在阳光下制造淀粉”的实验中，将天竺葵黑暗处理一昼夜后，用黑纸对叶片的一部分进行两面遮盖，光照一段时间、脱色处理后滴加碘液，脱色时溶解叶绿素的液体及滴加碘液后叶片变蓝的部位分别是（　　）