Final answer:
Ben Bernanke, the Fed chairman from 2006 to 2014, authored a book on the Great Depression and is the correct answer to the question (a).
Step-by-step explanation:
The current Fed chairman that authored a book on the Great Depression is Ben Bernanke. From 1987 until early 2006, Alan Greenspan was the Chair of the Federal Reserve, followed by Ben Bernanke from 2006 until 2014. Bernanke has written extensively on the Great Depression as part of his academic work before becoming Fed chair. Janet Yellen succeeded Bernanke and served as chair from 2014 to 2018. As of the current period, Jerome Powell is the Fed chairman, having been nominated for a second term by President Biden and confirmed in early-2022.
Therefore, the correct answer to the question is: a) Ben Bernanke.