Together, the United States and Brazil produce more than 70% of the world’s alcohol. In the United States, alcohol is produced mostly from corn, and is also (36) with a high tax. Brazilian alcohol (37) is mainly from sugar cane. In Brazil, about 40% of all motor fuel is alcohol. Many Brazilians drive flex-fuel (38) , which can use either gasoline or alcohol. As this (39) is so successful, General Motors has stopped making cars for the Brazilian market that only use gasoline. In the United States, vehicles that nm on pure alcohol are (40) . But most cars can run on a mixture of gasoline and 10% alcohol. Some states require (41) alcohol and gas to cut pollution. Yet the use of an important food crop for fuel has led to (42) . Alcohol now makes up about 12% of all corn use in the United States. At (43) growth rates, that could nearly double by 2015. Some people worry that (44) . Therefore, fuel researchers are exploring additional ways to make alcohol. (45) . This material is known as stover. But stover protects against soil loss to wind and water. (46) .