--- Mr Smith, please teach me how to dra
题型：选择题
问题：
--- Mr Smith, please teach me how to draw on the computer today.
---Oh, no._______. You have to get familiar with the keyboard first.
A．Learn to walk before you run
B．It's never too old to learn
C．A good beginning is half done
D．The early bird catches the worm
，OA之间的距离为
，一同学在实验报告中称，他测得
,
,据此可得：
，
，在误差允许的范围内两者相等。但老师认为数据失实，其理由是 。