后来发展为著名瓷都的景德镇兴起于（　　）

（Ⅰ）设 $\overrightarrow{OA}=a,\overrightarrow{OB}=b$ ，若 $\overrightarrow{OM}=\frac{3}{4}\overrightarrow{OA}$ ，用a，b表示 $\overrightarrow{CM},\overrightarrow{CN}$ ；

（Ⅱ）求 $\overrightarrow{CM}\cdot \overrightarrow{CN}$ 的取值范围．

阅读短文，下列问题

B

    Is there something strange high up in the world's tallest mountains? If so, is it a big bear（熊）? Is it a monkey? Or is it a kind of man?

    No one knows.This mystery（谜）has puzzled（困惑）the world（世界）for years.

    In 1887, a mountain climber found large footprints（脚印）in the snow.They looked like the footprints of a very large man. But men don't walk without（无、没有）shoes in the snow!

    In 1906, another climber saw more than footprints. Far off, he saw a very large animal standing on two legs. When he watched, it ran very quickly.

    Fifteen years later newspapers had new stories about the “something”. A mountain climber said he had seen the “Snowman” walk slowly across（穿过）the snow, far below him. He said it looked like a very large man.

    From then on, more and more people had stories to tell. But not until 1951 did a mountain climber bring back pictures of large footprints. The pictures showed that the Snowman walked on two legs. So it was not a bear or a monkey. Could it be an ape（猿）man? The mystery grew! And the mystery keeps growing. Someday we may find out just what it is that makes the large footprints.