文章献给准备过英语专业四级的同学，给同学一点经验，希望大家考试成功。
is a contest! Who will win? A bluebird and sparrow both compete for space to build their nests. A fast-growing maple tree and slower-growing dogwood compete for the sunlight they both need. Oil competes with coal and nuclear power as an energy source for electric power plants.
There is a problem. There is a limited amount of space for birds, sunlight for trees, and energy for people! If we do not cut back on our uses of some of our resources, someday they will be gone!
How can we use energy today and know we will have enough to go around in the future? We can choose alternate, or replacement, energy resources. It takes the earth millions of years to create coal, oil, and gas. They are nonrenewable resources.
Solar energy, wind energy and water energy are renewable. What other ways we conserve our resources? How can we make sure there is always enough to go around?