Question

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.

8

This leads to two of the strongest arguments against the increasing use of biofuels. First, changes in land use may create food shortages. One consultant says that replacing just 5% of diesel in the United States with biodiesel would require switching 60% of the nation's soy crops from food to fuel. As the demand for corn or soybeans goes up and the supply available for food goes down, the price of food goes up.

9

Second, using current technology, biofuels take more energy than they give! In a study reported in 2005, researchers studied various biofuels. They calculated the ratio of energy inputs to output. Inputs are what it takes to produce the biofuel, such as the energy to run tractors, trucks, and factories. Output is the energy users can get from the biofuel. This particular study showed that it takes 129 units of energy to produce enough ethanol to generate 100 units of energy.



Select the TWO approaches the author uses in paragraph 9 to explain the difference between energy inputs and output.


The author provides simple definitions.


The author describes the production process.


The author uses equipment as a contrast.


The author clarifies what energy units are.


The author references a 2005 study.

Answer 1

- The author provides simple definitions.
- The author references a 2005 study.