Difficult words: fuel (materials which people burn and they produce heat or power), gravity (the force which pulls things towards the Earth), technology (machines, devices, and ways of doing things).

困难的词语：燃料（人们燃烧并产生热量或电力的材料）、重力（将物体拉向地球的力）、技术（机器、设备和做事的方式）。