became the world's largest single source of air pollution by the 1990s.
a. auto emissions
b. waste incineration
c. metal smelting
d. chemical emissions

The answer is C. Auto Emissions

Explanation:

In the 1990's cars were the new thing of the time and since they were older models they didn't and couldn't properly dispose of gasoline in a gas form that polluted the air until newer versions came out that consumed less gasoline and produced less pollution.

an interest group is an organization whose members share common concerns, and try to influence government policies that impact those concerns. elected officials frequently complain about the influence of "special interests" on american politics.

william mckinley

ulysses s. grant

benjamin harrison

by the way what grade r u in k12?