your right it only takes 15s to find the classic example
a) envoy: embassy
b) martyr : massacre
c) oarsman :regatta
d) horse: stable
This is a poor example of what you're trying to argue. I was a white, upper middle class kid, well educated, and I would have had no idea what a regatta was back in high school. Take all the white, upper middle class kids from the south and midwest (or really anywhere outside of a large coastal city), and I'm certain that they would probably fare no better on this question then a similarly wealthy/educated black student.
By the way, even though I had never heard the word "regatta" while in high school I probably would have still gotten the question correct by using process of elimination. That's just a reflection of general intelligence and being a good test taker, nothing to do with race.