简述基本单位和导出单位的关系。
参考答案:
基本单位是约定为彼此独立的,而导出单位是用基本单位和比例因素表示的,为某些导出单位表示方便,它用专门的名称和符号表示。
用括号内所给单词的适当形式填空
1. It's five o'clock. The students __________(play) football on the playground.
2. You __________(not pass) the exam if you don't work hard enough.
3. The baby is sleeping. Could you please stop __________(make) so much noise?
4. This machine __________(use) for cleaning the house.
5. The man spoke very slowly. He wanted me __________(understand) what he said.
图是某物体运动的v-t图像,则下图中能相应表示出该物体运动的s-t图像的是
A.
B.
C.
D.