Read and write. (看图写句子)

1. He is _________________________________Hold on, please.

2. My father is_______________________________________.

3. The kangaroos_____________________________________.

4. She_____________________________________________.

5. -Are they______________________________. Yes,  they are.

有一输送流体的管道是由两段粗细不同的管子连接而成，其中粗管段的流速为8米/秒，管通径面积为7850平方毫米，细管段的流速为12米/秒，求细管段的管子内径是多少？