Wastewater comprises about ________ percent of the flow of U.S. rivers.
A) 8
B) 25
C) 15
D) 50
E) 33
Question 2
Since the 1960s, as a result of automobile modifications (as well as other factors), carbon monoxide emissions in the U.S. have declined by more than three-fourths and ________ emissions by more than 95 percent.
A) nitrogen oxide and hydrocarbon
B) nitrogen hydroxide and oxygen
C) nitrogen and oxygenated
D) sulfur dioxide and bicarbonate
E) hydrocarbon and sulfur dioxide