Professor Yarnofsky wonders whether recent acts of airline terrorism have made the public more fearful of airline flight. He secures records of the amount of flight insurance that people have purchased via machines at the airport, and compares the records of insurance purchases before the last hijacking to purchases after the last hijacking. Professor Yarnofsky has employed a(n) research method.

archival research method

Explanation:

Professor Yarnofsky wonders whether recent acts of airline terrorism have made the public more fearful of airline flight. He secures records of the amount of flight insurance that people have purchased via machines at the airport, and compares the records of insurance purchases before the last hijacking to purchases after the last hijacking. Professor Yarnofsky has employed an archival research method.

Archival research is a method of research which involves searching out information or data from existing records or archives in the carrying out of the study. The advantage or archival research is that it is less expensive as the data needed are already available in storage, secondly, the biases observed in research studies involving human subjects is non-existent in archive research. There is also a lot of data in archive research which increase the accuracy of the results

i am pretty sure it is d.