2x＋7x＋2.1=12

x=____

心理学实验表明，只靠耳朵听的知识，3个小时后只能记住65%左右；只靠眼睛看的知识，3个小时后可保持70%左右，3天后能记住30%左右；如果视听结合获得的知识，3个小时后能保持85%左右，3天后能保持70%左右。从哲学上看，这个实验告诉我们要提高记忆力需要（   ）

在横线上填上“>”“<”或“=”

9分米____90厘米     4200米____ 4千米     18分米 ____ 20厘米

根据短文理解选择答案。

     My name is Mary. I'm eleven. I'm from China. My mum and dad work in a factory. They go to work from Monday to Friday. I have a sister. Her mane is Amy. We look like each other very much and we like to help each other. She and I are middle school students.

     Amy and I are in the same school. I' m a good student in my class. There are forty-two students in my class, twenty boys and twenty-two girls. We have our lessons from eight o'clock in the morning to four o'clock in the afternoon. My English teacher Miss Green, is from England. She is a good teacher. We have five English classes in a week. Now we can say a hundred words and play games in English, We like English and we like our English teacher.