一个物体在一条直线上运动，已知在8秒钟内匀速通过320米，则此物体在第5秒钟时的速度是______米/秒．此物在前半路程中的速度是______米/秒．

After he gave a report about the school, Mr White____ the visitors around it.

A．went on to show

B．went on showing

C．went on with showing

D．kept on showing