如果不靠外力相助,人类很难单凭自身的力量提起建筑材料,或将重物搬上货车或者轮船。起重机就是解决这个问题的一个好帮手。起重机发明于公元前515年的古希腊。正如很多其他的希腊发明一样,起重机也慢慢地被罗马人所接受,他们甚至还改进了希腊人的设计。在引擎和电动机相继被发明后,起重机又有了新的 If we do not rely on external help, it is very hard for human beings to lift building materials by their own strength or carry heavy loads on trucks or ships. Crane is a good helper to solve this problem. Crane invented in 515 BC in ancient Greece. Like many other Greek inventions, the cranes are slowly being accepted by the Romans, who have even improved the design of the Greeks. After the engine and motor have been invented, the crane has a new one