Nativists were people who believed that what group of people were hurting americans?

They believed that the immigrants were hurting Americans(more strictly, immigrants that were not descendants of the original 13 colonies). A significant example is the Know Nothing or American Party of the 1850s. An earlier example is the Federalist Party which extended the time required to be American to 14 years through the Alien and Sedition Acts.

The correct answer is b