Final answer:
RESPA applies to residential loans for one-to-four family properties and does not typically cover commercial loans, residential investment properties, or vacant lot loans.
Step-by-step explanation:
The Real Estate Settlement Procedures Act (RESPA) applies to federally related mortgage loans. This primarily includes residential loans that are secured by a mortgage placed on a one-to-four family residential property. Therefore, the correct answer is a: Residential loans. RESPA does not cover commercial loans, investment properties such as condos or duplexes, or vacant lot loans unless they will be used for a residential purpose and a mortgage is obtained.