The young boy helped himself to a watch lying on the pavement. A. The young boy couldn't help seeing a watch left abandoned on the pavement. B. When the young boy saw a watch on the pavement,

The young boy couldn't help seeing a watch left abandoned on the pavement.

When the young boy saw a watch on the pavement, he quickly asked for help.

The young boy took the watch which was left abandoned on the pavement.

Seeing a watch on the pavement, the young boy would definitely pick it up.