单词注解：

precrease:预褶 就是pre-crease

diagonally:in a diagonal manner

kite:a bank check that has been fraudulently altered to increase its face value；a bank check drawn on insufficient funds at another bank in order to take advantage of the float

valley:a long depression in the surface of the land that usually contains a river

bisector:二等分物,二等分线

beak:beaklike mouth of animals other than birds (e.g., turtles);horny projecting mouth of a bird;informal terms for the nose

parallel: be parallel to; make or place parallel to something; duplicate or match