Final answer:
The National Transportation Safety Board (NTSB) is the agency responsible for investigating and determining the probable cause of airliner crashes in the United States, not the FAA, ICAO, or NASA. The correct option is A.
Step-by-step explanation:
The agency primarily responsible for investigating and determining the "probable cause" of airliner crashes in the United States is the National Transportation Safety Board (NTSB). The NTSB is an independent U.S. government investigative agency that handles all civil transportation accident investigation, which includes aviation, highway, marine, pipeline, and railroad accidents.
The Federal Aviation Administration (FAA) is responsible for regulating and overseeing all aspects of American civil aviation, while the International Civil Aviation Organization (ICAO) is a specialized agency of the United Nations that sets global aviation standards and recommends practices.
NASA, which stands for National Aeronautics and Space Administration, is primarily associated with the nation's civilian space program and for aeronautics and aerospace research. When it comes to aviation accidents, it's the NTSB that steps in to conduct an investigation into the crash.
Hence, Option A is correct.