21.The word “crucial” in line 3 is closest in meaning to (A) obvious (B) unbelievable (C) important (D) desirable

23. According to the passage, why was the Civil War a stimulus for mechanization? (A) The army needed more grain in order to feed the soldiers. (B) Technology developed for the war could also the used by farmers. (C) It was hoped that harvesting more grain would lower the price of grain. (D) Machines were needed to replace a disappearing labor force.