I can't find out anything about this one Please help.
The increase in the use of unleaded gasoline is thought to be responsible for a ___% decrease in the amount of lead in the Mississsippi River in the last decade.
a. 10
b. 20
c. 30
d. 40
e. 50
I went to google.com and searched on mississipi river lead content. Got this first this out. Your answer is in the abstract.
http://www.sciencemag.org/cgi/content/abstract/230/4724/439