Which of the following is a primary source?
a. a biography of a historical figure
b. a history textbook
c. old newspaper clippings
d. personal interview with an eyewitness

The primary source would be D: Personal interview with an eyewitness.

Primary source is known data gathered in first-hand basis. A personal interview with an eyewitness is a first-hand data because the information exactly came from the person who actually saw what happened on that certain moment. The rest of choices were second-hand sources. Biography maybe directly from a person, but another made and wrote the biography. History textbook could be a collection of hundreds of years texts that meant more sources, same with old newspaper clippings.