能正确表示下列反应的离子方程式为：（      ）

五位中国学生要去美国留学，他们想要找住家。请仔细阅读第1-5题中的学生的个人情况说明，并从A至F六个选项中，帮助他们选择最适合的住家（其中一项为多余选项）
____ Zhang Chao likes Chinese food. He hopes his host family speak a little Chinese.
____ Li Wei likes doing sports. He wants to live near a park.
____ Liu Yong hopes to live near his school---Reading School. He prefers a bed room with a bathroom
____ Chen Yao wants to live in a big bedroom cheaper than ￡350 a month. She can’t stand pets.
____ Hu Mei loves pets. She would like a bedroom cheaper than ￡220 a month.

2×（－$\frac{1}{2}$）的结果是（     ）

图上1厘米代表实地距离100千米，用数字式比例尺表示是：（　　）