Question

Most people agree that the world cannot continue to use more and more fossil fuels each year. Petroleum, coal, and natural gas are nonrenewable resources; sooner or later they will run out. Also, the use of these fossil fuels releases carbon dioxide (CO2), a greenhouse gas that affects the climate. And because only certain places in the world have petroleum deposits, these oil-rich countries gain international power through control of this resource. Replacing fossil fuels with biofuels is widely touted as a solution to all these woes.

2

Biofuels are energy sources made from plants. Building a campfire with sticks and logs is a simple example of using a biofuel. Today, the world's leading biofuel is ethanol made from corn grown in the United States. Other biofuels include ethanol from sunflowers and biodiesel from soy, switch grass, or palm oil.

3

According to the hype, biofuels are superior because they are renewable; a new crop grows every year. Burning biofuels releases less CO2 than burning gasoline or diesel. And of course plants grow in almost every inhabited part of the world. A closer look at these claims, however, shows that they ignore the real costs of biofuel to the economy and to the environment.

4

Because of high and increasing demand for biofuels, big agriculture companies (agribusinesses) are choosing to concentrate on a single biofuel crop. In the United States this means growing more and more corn for ethanol. Corn requires a great deal of water. A study reported in 2009 that irrigation to grow more corn for ethanol was putting stress on the water supply in the Great Plains and the central Southwest.

5

Corn also takes a lot of nitrogen from the soil as it grows. For centuries, farmers have known to counter this by rotating crops. After a year of planting corn, a farmer might plant a different crop the next year in order to put nitrogen back into the soil. To meet the high demand for ethanol, agribusinesses prefer to apply nitrogen-rich fertilizers so they can continue to plant corn year after year.

6

Using too much fertilizer in this way pollutes the water and the air. Excess fertilizer runs off the fields with rainwater, ending up in the water supply. In lakes, it causes algae blooms, which harm aquatic plants and animals. In drinking water, too much nitrogen is bad for babies' health. Additionally, some of the excess nitrogen remains in the soil. Bacteria in the soil can change it chemically and release it into the air as nitrous oxide, a powerful greenhouse gas. Nobel Prize winner Paul Crutzen argues that nitrous oxide has been a major factor in global warming.

7

While almost every region has plants, not all biofuel crops are equal. Palm plantations in Indonesia yield some 635 gallons of vegetable oil per acre. By comparison, cornfields in the United States yield only 18 gallons per acre. Some of the most efficient biofuel crops grow best in the tropics, where many countries are very poor. To meet growing demand, tropical forests are being cut down and farm fields taken out of food production in countries that can least afford these losses.Which sentence BEST supports the statement that increasing the use of biofuels harms the environment?


the fourth sentence of paragraph 1


the fourth sentence of paragraph 4


the fourth sentence of paragraph 5


the fourth sentence of paragraph 7

Answer 1

the fourth sentence of paragraph 4