The richest discovery in the history of mining occurred in 1873. This so-called "Big Bonanza" made

_______ the richest man in the world.
A. John Mackay
B. Henry Sutter
C. John Placer
D. Henry Comstock

Is it A?

Yes!

Yes, the correct answer is A. John Mackay. John Mackay became the richest man in the world as a result of the "Big Bonanza" which occurred in 1873. To determine the correct answer, you could have used various methods like conducting research, referring to historical records or books, or consulting reliable sources such as reputable websites or encyclopedias.