如图，在⊙O中，弦AB垂直平分半径OC，垂足为D，若⊙O的半径为4，则弦AB的长为____．

—My favourite class is _______.

—In this class I can play football.

选择恰当的答语（  ）

从动物行为的获得途径看，“鹦鹉学舌”和“孔雀开屏”分别属于（    ）

阅读下文，回答问题
                                                                                                  On the beach
    It is a fine day. A lot of people go to the beach to enjoy sunshine. Some people are swimming like fishes in the sea. On the beach，some young people are playing volleyball.
    Some of them are lying under the coconut trees. And some old people are chatting with each other. What are the children doing? Look! They are making castles with spade and sand. They are having fun。
⑴⑵⑶⑷⑸根据短文内容，判断正误；⑹根据短文内容填空。