The Equal Credit Opportunity Act (ECOA) prohibits lenders from discriminating against applicants on the basis of which of the following?

Correct answer: National origin

ECOA (implemented by Regulation B) prohibits credit discrimination based on race, color, religion, national origin, sex, marital status, age, or because an applicant receives public assistance. National origin is explicitly listed as a protected class. Credit score (A) and DTI ratio (B) are legitimate underwriting criteria lenders may use. First-time homebuyer status (D) is not a protected class under ECOA — lenders may treat first-time buyers differently from experienced buyers in terms of program eligibility.