---- Mom , I was the first to reach the top of the mountain .

--- Good job, Jack! I 'm ______ of you.

A．careful.

B．proud.

C． tired

D．afraid.

明朝初期是当时世界上的一个强国，郑和下西洋是其突出表现。郑和下西洋所体现出的当时中国外交准则是   

A．闭关锁国

B．恃强凌弱

C．友好交往

D．自由贸易