有诗写道：“迷雾云遮难敞亮，宇寰久夜盼骄阳。柏宅楼上龙聚首，湘水岸边船启航。初战娄山标魄力，四夺赤水过长江。行程二万通华北，□□□□挽国邦。”根据上下文的意思，□□□□处应该填写：（   ）

A

    Look! This is a picture of my teacher's family. This is Mr. Smith.  He  is my English  teacher. His wife is a doctor. She is nice. They have a son and a daughter. The boy's  name is Sam and the   girl's name is Kate. They are students. They are in the same school. They go to school on their bikes. Look! The son is like his mother. The daughter is like her father. Now they are all in China and can speak Chinese. They love China.

已知函数f（x）=tan（2x+$\frac{\mathrm{\pi }}{4}$），求f（x）的定义域与最小正周期．