This is the life of someone who wrote little, spoke little, and about whom there are few memories. Yet if anyone's life is worthy of a biography it is surely Abram Petrovich Gannibal, an African slave adopted by Peter the Great, who studied mathematics and cryptography before training as a military engineer, spied for the tsar in Paris, became an expert in fortification, was sent to siberia, became the governor-general of Tallinn, and finally retired to an estate in northern Russia as the owner of slaves himself.
These days he is best known as the great grandfather of Alexander Pushkin, whose family liked to think their illustrious forebear was an Abyssinian prince, and a direct descendant of the legendary Carthaginian general whose name he boldly adopted (spelling it in the Russian way with a "g"). It was not until the 1990s that an enterprising scholar from Benin was able to challenge centuries of Russian racism and suggest that Gannibal in fact came from black Africa.
Having traveled to Cameroon and paddled up-river in a 30-foot wooden boot to interview the Sultan of Logone, the intrepid Hugh Barnes lends credence to this theory with a tantalizingly plausible interpretation for the mysterious word "Fummo" (Kotoko for "homeland") to be found underneath the elephant portrayed on the family crest. Mr. Barnes does far more than just "join up the dots" between Pushkin's unfinished novel about his ancestor and its subject. The result is not merely the first detailed account in English of this remarkable life, but the fullest in any language. It is a fascinating read.
With this book, the fruit of research in an impressive list of obscure archives, Mr. Barnes not only joins the ranks of those journalists able to give academics a good run for their money, but also shows him-self to be a travel writer of distinction. The story of his quest to discover Gannihal's identity in places as far-flung as Novoselengisk on the Chinese border, and Pskov at the other end of the Russian empire, is engagingly told. With so little biographical material to go on (even the fabled portrait of Gannibal turns out to be that of a white man when it is restored), the dots have inevitably to be joined up with a degree of speculation. Just occasionally it leads the author astray--the Winter Palace, for example, was painted first yellow and then crimson before finally acquiring the "icy turquoise facade", which Mr. Barnes claims greeted Gannibal when he received his dismissal from Catherine the Great in 1762.
While plenty of evidence is marshaled to show that Gannibal was the first black intellectual in Europe, his personality remains frustratingly elusive. Nevertheless, this biography of the Russian Othello does much to recast our understanding of 18th century Russian life.
What is the purpose of the passage？

A. To give us a portrait of a legendary person--Abram Petrovich Gannibal.
B. To reveal the origin of Gannibal.
C. To indicate the connection of Pushkin and Gannibal.
D. To introduce Hugh Barnes's research work and his book on Gannibal.