1. 四边形   vertex   quadrangle   pyramid   ellipse   Hint Half-n-half Clue   2. 五边形   plane   pentagon   prism   polygon   Half-n-half Clue   3. 四方形   parallel lines   perpendicular lines   quadrilateral   plane   Half-n-half Clue   4. 凸面   heptagon   ray   oval   convex   Half-n-half Clue   5. 平行的线   oval   rhombus   straight line   parallel lines   Half-n-half Clue   6. 飞机   vertex   parallel lines   plane   prism   Half-n-half Clue   7. 半球   prism   convex   rhombus   hemisphere   Half-n-half Clue