Final answer:
Nativists made use of "scientific" ideas to give reasons that some races were weaker than others.
Step-by-step explanation:
The nativists made use of "scientific" ideas by giving reasons to say that some races were weaker than others (option C). They believed in the concept of eugenics, which promoted the idea that there were superior and inferior races based on characteristics such as intelligence and physical attributes. Nativists used these ideas to justify their opposition to immigration, particularly from non-white and non-Protestant groups.