The reason ____ his coming to China is _____ he wants to study in China.   [ ]

A. why; that    

B. why; because    

C. for; that    

D. for; because

路由器可以包含一个特殊的路由。如果没有发现到达某一特定网络或特定主机的路由，那么它在转发数据包时使用的路由称为______路由。