1. 卵形   pentagon   convex   plane   oval   Hint Half-n-half Clue   2. 飞机   segment   polygon   pyramid   plane   Half-n-half Clue   3. 四边形   prism   polygon   quadrangle   ellipse   Half-n-half Clue   4. 菱形   polygon   perpendicular lines   rhombus   parallel lines   Half-n-half Clue   5. 多角形   pyramid   polygon   vertex   concave   Half-n-half Clue   6. 五边形   pentagon   heptagon   ellipse   parallelogram   Half-n-half Clue   7. 四方形   oval   parallelogram   quadrilateral   heptagon   Half-n-half Clue