Many people think the search for cleaner energy leads only to renewable resource

Many people think the search for cleaner energy leads only to renewable resources like sun, wind and water. But it __48__ leads to a fossil fuel. Natural gas is considered __49__ cleanest of the fossil fuels, the fuel created by plant and animal remains over millions __50__ years. Burning it releases fewer pollutants __51__ oil or coal. The gas is mainly methane (甲烷). It produces half the carbon dioxide of other fossil fuels. So __52__ may help cut the production of carbon gases linked to climate change.

Russia is first in __53__ are called "proved reserves" of natural gas. The United States is sixth. Over the years, big oil __54__ gas companies recovered much of the easily reached supplies of gas in America. They drilled straight down into formations where gas collects. __55___these supplies were used up, big drillers looked for similar formations in other countries.

试题答案

 also, the, of, than, it, what, and, As/Because