正三角形ABC的边长为2，D，E，F分别在三边AB，BC，CA上，D为AB的中点，DE⊥DF，且DF=$\frac{\sqrt{3}}{2}$DE，则∠BDE=____ 

阅读判断。
    Jenny, Danny, Kim and Steven are good friends. Jenny and Kim are reading books in the library. Where are Danny and Steven? Look! They are playing a game on the playground. Who is in the classroom? It's Mr. Wood.

This cake is really big. _______ share it.

人类文明的发展，离不开各种文明的交流和碰撞。下列被誉为古代“东西方交流的使者”的是（ ）       

下列说法正确的是                                                                                        （   ）