What is a common name for trefoil, a plant with three leaflets?

A 1937 commemorative half dollar honored which bloodiest one-day battle of the Civil War? A commission established in 1987 has sponsored what events every four years since 1988? Which common adverb is also the acronym of a large feminist group? Which common mineral is used to make plaster of Paris? Which Communist leader said in 1938, "Political power grows out of the barrel of a gun"? Which slow cooker brand name was trademarked by the Rival company in 1971? A compass needle points toward which north pole? A competitive speed skater since age 4, which American won her first Olympic gold medal in 1988?