单项选择题Cement was seldom used in building during the Middle Ages.
单项选择题Medicine depends on other fields for basic information, particularly some of their specialized branches.
单项选择题Since the Great Depression, the United States government has protected farmers from damaging drops in grain prices.
单项选择题We shall take the treasure away to a safe place.
单项选择题Gas does accumulate in the mines around here.