单项选择题
The most important result of the Lewis and Clark expedition was that it enabled the United States to claim the Oregon region.
单项选择题 The cylindrical shape of a cactus reduces moisture loss.
单项选择题 By 1900, many municipalities had begun to restrict the use of automobiles in order to en- sure pedestrian safety.
单项选择题 Over thirty cities around the world boast more than five million residents.
