The girl is      shy.

Here are summer activities in museums.

The Postal Museum

Date: July 16 to July 22

Age: 11—13

    Would you like to join us this summer vacation? You can learn about the history of stamps (邮票)and design (设计) a stamp yourself. You can also enjoy many beautiful pictures in our museum.

Tel: 965-0403

The Air and Space Museum

Date: July 24 to July 30

Age: 8—11

    If you like activities about air and space, please come here. It's a good place to make and fly your own paper plane, watch an IMAX movie, and climb into a real plane.

Tel: 654-0937

The Science Museum

Date: August 7 to August 13

Age: 9-12

    You can experience video arts, play computer games about future cities, and ask robots questions here. It will be wonderful! Have fun!

Tel: 357-3039

The Building Museum

Date: August 15 to August 22

Age: 13-15

    Want to enjoy design challenges (挑战)? Come and join us. You can go on trips to some famous buildings, learn to design your own room, and build small houses,

Tel: 272-0561

根据材料内容选择最佳答案。

如图，在Rt△ABC中，BC=2，∠BAC=30°，斜边AB的两个端点分别在相互垂直的射线OM、ON上滑动，下列结论：

①若C、O两点关于AB对称，则OA=2 $\sqrt{3}$ ；

②C、O两点距离的最大值为4；

③若AB平分CO，则AB⊥CO；

④斜边AB的中点D运动路径的长为 $\frac{\pi }{2}$ ；

其中正确的是____（把你认为正确结论的序号都填上）．