Write a question about the following article: US imports decreased 66% from $4.4 billion (1929) to $1.5 billion (1933), and exports decreased 61% from $5.4 billion to $2.1 billion. GNP fell from $103.1 billion in 1929 to $75.8 billion in 1931 and bottomed out at $55.6 billion in 1933. Imports from Europe decreased from a 1929 high of $1.3 billion to just $390 million during 1932, while US exports to Europe decreased from $2.3 billion in 1929 to $784 million in 1932. Overall, world trade decreased by some 66% between 1929 and 1934.

Question about the article:
How many years total saw a large world trade decrease of 66%?