已知一粒大米的质量为0.000021千克,把0.000021用科学记数法表示为______.
0.000021用科学记数法可表示为2.1×10-5.
故本题答案为:2.1×10-5.
阅读理解。
Jim is from the USA. But his father, mother and he are in China now. His mother is a teacher. His father is a
doctor. Jim is in Class 7, Grade 8. He is 13. His mother is my English teacher. I'm Zhang Jun. I'm in Class 8,
Grade 7. I'm 13, too.
根据短文内容,选择正确答案.
1. Jim's family (家庭) is from _______.
A. America
B. China
C. Japan
2. Who is in Grade 8?
A. Li Lei.
B. Jim.
C. His mother.
3. Who is in Class 8?
A. Zhang Jun.
4. How old is Jim?
A. 7.
B. 8.
C. 13.
5. Are Zhang Jun and Jim of the same age (同龄)?
A. Yes, he is.
B. Yes, they are.
C. No, they aren't.
A.幻灯机
B.照相机
C.平面镜
D.放大镜