The keystone to what Henry Clay called the American System was A. abolishing slavery. B. a low tariff C. encouraging British competition. D. a high tariff.

The correct answer is D. a high tariff. This would mean that it would be a lot more difficult to import and earn money so people would produce their own American made goods, and in turn pay taxes for that in the US and this would fill up the national budget. Or at least that's how he envisioned it.