读“我国主要山脉和主要河流分布图”，回答下列问题。

（1）山脉M和河流R为我国重要的地理分界线，其中山脉M是____ ，河流R是____ ，它们是我国____ 地区和____  地区的分界线。
（2）我国濒临的海洋，从北到南依次为渤海、黄海、东海和南海，图中P海为____ ，Q海为____ 
（3）我国沿海地区集中了长江三角洲、辽中南、京津唐和珠江三角洲四大工业基地，图中①____ 工业基地，②____ 工业基地，③____ 工业基地，④____ 工业基地。

    Chinese writing began thousands of years ago. According ____ an ancient story, a man named Cang Jie invented Chinese writing. One winter day while he was hunting, he saw the ____(track) of animals in the snow and ____(observe) that the appearance of each one was different. Then ____he got was that he could use different shapes ____(represent) different objects. The ____(one) Chinese characters were drawings of physical objects. Some characters ____(simplify) and others have been made ____(difficult) over time.____, as a whole, the characters have ____(gradual) developed from drawings into standard forms.

____

(从上到下依次填写)