注意首字母大小寫，不含標(biāo)點(diǎn)符號 ___1___, and some sources of energy are being used up very quickly. So scientists and technicians are trying to find new ways to produce power. __2___, cow manure and garbage have become energy sources. But probably the most promising source of energy is solar heat. ___3___. If this were done,___4___.
The need for power increases every day Nuclear energy Some scientists suggest using these different sources of energy together it would be a way to create all of the power people need.