Which of the following is NOT true of U.S. foreign trade? （）
Canada is the largest single source of goods imported by the United States.
Outside of North America, Asia is the largest source of imports.
The U.S. share of world trade has decreased in recent years.
Whenever the American economy is in trouble, the economy of other countries is affected.
在北美之外，亚洲并不是美国最大的进口来源。
