The map below shows the location of some natural resources in North America. The map shows various natural resources across North America. In Mexico, the map indicates copper, silver, and iron are found. Across the United States, iron, oil, coal, copper, gold, and silver are found. In Canada, lead and zinc, coal, copper, oil, iron, gold, silver, and uranium are found.
© 2011 FLVS

According to the map, which natural resource can only be found in Canada?

Oil
Silver
Coal
Uranium