9去掉____个0.1是8.1。

     Plants are very important. This is because plants can make food from air, water and sunlight. Animals and people can not make food from air, water and sunlight. Animals can get their food by eating plants and animals. People get their food by eating plants and animals, too. So animals and people need plants in order to live. This is why there are so many plants around us. There are two kinds of plants: flowering plants and non-flowering plants. You can know some trees from their flowers and fruits. Non-flowering plants do not grow flowers. You can not see many non-flowering plants around you. If you look carefully at the plants around us, you will find that there are many kinds of plants. Some plants are large and some are small. Most of them are green. Thanks to the plants around us we can live on the earth.

当消费者的合法权益受到侵害时，消费者可以（    ）
①向公安机关申诉                        ②向当地消费者协会投诉
③与经营者协商解决                     ④向人民法院提起诉讼

（Ⅰ）根据以上尺规作图的过程，求证：四边形ABEF是菱形；

（Ⅱ）若菱形ABEF的周长为16，AE=4 $\sqrt{3}$ ，求∠C的大小．