想一想，填一填。
6÷2=____
30÷5=____
20÷5=____
想：二____得六
想：五____三十
想：____五二十
It's very useful to ______the correct answers next to the mistakes.
它“使人们的认识由低速领域扩大到高速领域，由宏观领域延伸到宇宙领域，人们第一次深刻地认识到时间、空间和物质的运动相互依赖。”“它”指的是（ ）
you can't answer the question, perhaps we'd better ask someone else.
