What is a question about this article? If the question is unanswerable, say "unanswerable".

Canada has the world's largest deposit of natural bitumen in the Athabasca oil sands and Canadian First Nations along the Athabasca River had long used it to waterproof their canoes. In 1719, a Cree Indian named Wa-Pa-Su brought a sample for trade to Henry Kelsey of the Hudson’s Bay Company, who was the first recorded European to see it. However, it wasn't until 1787 that fur trader and explorer Alexander MacKenzie saw the Athabasca oil sands and said, "At about 24 miles from the fork (of the Athabasca and Clearwater Rivers) are some bituminous fountains into which a pole of 20 feet long may be inserted without the least resistance."

Alexander MacKenzie was a oil trader and saw the oil sands in what year?
unanswerable