★ First——invented machines
Event :Thousands of years ago，people invented machines.
Reason :It's hard to do it by manpower alone.
Event :People invented Levers.
Reason :Stop the beast in the night.
Result :At that time, people's work became easier and the lever became a kind of machinery.
ps:It's about the lever
Events :People began to move heavy objects with rollers.
Reason :People find it easier to move heavy objects with rollers.
ps:There is a word "吴" in the name of the building
Events :The Egyptians built pyramids with ramps.
Result :Today, ramps are used in many places.
Events :People(Who is he/she?)invented the screws.
Reason :We use it to fix(除了维修，还有固定的意思) sonething.
ps:We talked about it before.
I think he is a genius!
Today, we learned the development of machinery.Let's sort out its development:
OK, that's all the content of today's course.Thank you for all of you guys!