instruction:
This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
question:
Passage: West of the Rocky Mountains lies the Intermontane Plateaus (also known as the Intermountain West), a large, arid desert lying between the Rockies and the Cascades and Sierra Nevada ranges. The large southern portion, known as the Great Basin, consists of salt flats, drainage basins, and many small north-south mountain ranges. The Southwest is predominantly a low-lying desert region. A portion known as the Colorado Plateau, centered around the Four Corners region, is considered to have some of the most spectacular scenery in the world. It is accentuated in such national parks as Grand Canyon, Arches, Mesa Verde National Park and Bryce Canyon, among others. Other smaller Intermontane areas include the Columbia Plateau covering eastern Washington, western Idaho and northeast Oregon and the Snake River Plain in Southern Idaho.
answer:
What is the name of the plateau that lies east of the Rocky Mountains?


question:
Passage: Since World War II, aircraft carrier designs have increased in size to accommodate a steady increase in aircraft size. The large, modern Nimitz class of US carriers has a displacement nearly four times that of the World War II–era USS Enterprise, yet its complement of aircraft is roughly the same—a consequence of the steadily increasing size and weight of military aircraft over the years. Today's aircraft carriers are so expensive that nations which operate them risk significant political, economic, and military impact if a carrier is lost, or even used in conflict.
answer:
Why have aircraft carriers increased in size since World War I?


question:
Passage: Following a peak in growth in 1979, the Liberian economy began a steady decline due to economic mismanagement following the 1980 coup. This decline was accelerated by the outbreak of civil war in 1989; GDP was reduced by an estimated 90% between 1989 and 1995, one of the fastest declines in history. Upon the end of the war in 2003, GDP growth began to accelerate, reaching 9.4% in 2007. The global financial crisis slowed GDP growth to 4.6% in 2009, though a strengthening agricultural sector led by rubber and timber exports increased growth to 5.1% in 2010 and an expected 7.3% in 2011, making the economy one of the 20 fastest growing in the world.
answer:

When did the Liberian economy reach peak timber exports?