The Mackenzie River system is the second-longest in North America.

Discover Canada records this in one direct sentence about the Northwest Territories. The guide writes: The Mackenzie River, at 4,200 kilometres, is the second-longest river system in North America after the Mississippi and drains an area of 1.8 million square kilometres. The status the test wants is therefore true — the Mackenzie River system is the second-longest in North America.

Three precise commitments. Discover Canada commits the Mackenzie River to THREE specific facts: (1) its length is 4,200 kilometres; (2) it is the second-longest river system in North America after the Mississippi; (3) it drains an area of 1.8 million square kilometres. So the source pinpoints the named length, the named ranking, and the named drainage area.

The Mackenzie River system flows through Canada's North. Discover Canada commits the Mackenzie's named home to the Northwest Territories: the source's named description of the Mackenzie appears in the same passage that names Yellowknife as the named capital and "the diamond capital of North America." So the Mackenzie River system flows through the named diamond-rich Canadian north. The Northwest Territories is named as one of Canada's three Northern Territories, alongside Yukon and Nunavut.

The named Northern Territories are vast and sparsely populated. Discover Canada commits the Northern Territories to a specific named geographic share: "The Northwest Territories, Nunavut and Yukon contain one-third of Canada's land mass." So one-third of Canada's vast geography lies in the named Northern Territories — and the named Mackenzie River system drains a substantial named portion of that vast area. The Mackenzie's named 1.8-million-square-kilometre drainage is roughly equal to a large European country. The named Northern Territories' population is small but the geography is enormous. The named Mackenzie River system is North America's second-longest after the Mississippi — making it one of the most important named rivers in Canada and in the continent. So when the test asks whether the Mackenzie River system is the second-longest in North America, the source-precise answer is true.

The question is testing whether new citizens know the Mackenzie River's named ranking. Discover Canada commits to one named ranking: the second-longest river system in North America after the Mississippi. The right test answer matches that — true.

The wrong answer ("False") reverses the source — the Mackenzie River system IS the second-longest in North America. The named ranking is exact. Only the true answer matches.